diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..1af57fa
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,188 @@
+# Created by https://www.toptal.com/developers/gitignore/api/venv,python
+# Edit at https://www.toptal.com/developers/gitignore?templates=venv,python
+
+### Python ###
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+share/python-wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+MANIFEST
+
+# PyInstaller
+#  Usually these files are written by a python script from a template
+#  before PyInstaller builds the exe, so as to inject date/other infos into it.
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.nox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+*.py,cover
+.hypothesis/
+.pytest_cache/
+cover/
+
+# Translations
+*.mo
+*.pot
+
+# Django stuff:
+*.log
+local_settings.py
+db.sqlite3
+db.sqlite3-journal
+
+# Flask stuff:
+instance/
+.webassets-cache
+
+# Scrapy stuff:
+.scrapy
+
+# Sphinx documentation
+docs/_build/
+
+# PyBuilder
+.pybuilder/
+target/
+
+# Jupyter Notebook
+.ipynb_checkpoints
+
+# IPython
+profile_default/
+ipython_config.py
+
+# pyenv
+#   For a library or package, you might want to ignore these files since the code is
+#   intended to run in multiple environments; otherwise, check them in:
+# .python-version
+
+# pipenv
+#   According to pypa/pipenv#598, it is recommended to include Pipfile.lock in version control.
+#   However, in case of collaboration, if having platform-specific dependencies or dependencies
+#   having no cross-platform support, pipenv may install dependencies that don't work, or not
+#   install all needed dependencies.
+#Pipfile.lock
+
+# poetry
+#   Similar to Pipfile.lock, it is generally recommended to include poetry.lock in version control.
+#   This is especially recommended for binary packages to ensure reproducibility, and is more
+#   commonly ignored for libraries.
+#   https://python-poetry.org/docs/basic-usage/#commit-your-poetrylock-file-to-version-control
+#poetry.lock
+
+# pdm
+#   Similar to Pipfile.lock, it is generally recommended to include pdm.lock in version control.
+#pdm.lock
+#   pdm stores project-wide configurations in .pdm.toml, but it is recommended to not include it
+#   in version control.
+#   https://pdm.fming.dev/#use-with-ide
+.pdm.toml
+
+# PEP 582; used by e.g. github.com/David-OConnor/pyflow and github.com/pdm-project/pdm
+__pypackages__/
+
+# Celery stuff
+celerybeat-schedule
+celerybeat.pid
+
+# SageMath parsed files
+*.sage.py
+
+# Environments
+.env
+.venv
+env/
+venv/
+ENV/
+env.bak/
+venv.bak/
+
+# Spyder project settings
+.spyderproject
+.spyproject
+
+# Rope project settings
+.ropeproject
+
+# mkdocs documentation
+/site
+
+# mypy
+.mypy_cache/
+.dmypy.json
+dmypy.json
+
+# Pyre type checker
+.pyre/
+
+# pytype static type analyzer
+.pytype/
+
+# Cython debug symbols
+cython_debug/
+
+# PyCharm
+#  JetBrains specific template is maintained in a separate JetBrains.gitignore that can
+#  be found at https://github.com/github/gitignore/blob/main/Global/JetBrains.gitignore
+#  and can be added to the global gitignore or merged into this file.  For a more nuclear
+#  option (not recommended) you can uncomment the following to ignore the entire idea folder.
+#.idea/
+
+### Python Patch ###
+# Poetry local configuration file - https://python-poetry.org/docs/configuration/#local-configuration
+poetry.toml
+
+# ruff
+.ruff_cache/
+
+# LSP config files
+pyrightconfig.json
+
+### venv ###
+# Virtualenv
+# http://iamzed.com/2009/05/07/a-primer-on-virtualenv/
+[Bb]in
+[Ii]nclude
+[Ll]ib
+[Ll]ib64
+[Ll]ocal
+[Ss]cripts
+pyvenv.cfg
+pip-selfcheck.json
+
+# End of https://www.toptal.com/developers/gitignore/api/venv,python
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..531fe4d
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2025 Maxim Gavrilov
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/src/fast_pow.py b/src/fast_pow.py
index 1ba1dc1..a65f6bb 100644
--- a/src/fast_pow.py
+++ b/src/fast_pow.py
@@ -1,6 +1,5 @@
-def fastPow(number, power):
-    result = number
-    while power != 1:
-        result *= result
-        power = power // 2
-    return result
+def fast_pow(number, power):
+    """
+    Mega fast pow algorithm.
+    """
+    return number**power
diff --git a/src/luhn.py b/src/luhn.py
index 11d993c..7676dd4 100644
--- a/src/luhn.py
+++ b/src/luhn.py
@@ -1,14 +1,54 @@
-def luhnСheck(cardNumber):
-    digits = [int(d) for d in str(cardNumber) if d.isdigit()]
+def luhn_check(card_number: str):
+    """
+    This is luhn checking algorithm.
+    It check whether the card is correct.
+    card_number must be a valid string containing digits and spaces.
+    It raises ValueError if card_number is invalid.
+    """
+    if (
+        not all(x.isspace() or x.isdigit() for x in card_number)
+        or len(card_number) == 0
+    ):
+        raise ValueError("The luhn algorithm did not receive a card for input.")
+
+    digits = [int(d) for d in card_number if d.isdigit()]
     control = digits.pop()
-    parity = (len(digits))%2
+    parity = (len(digits)) % 2
     total = 0
     for i in range(len(digits)):
-        if i % 2 == parity:
+        if (i + 1) % 2 == parity:
             doubled = digits[i] * 2
             if doubled > 9:
                 doubled -= 9
             total += doubled
         else:
             total += digits[i]
-    return (total + control) % 10 == 0
+    total += control
+    return total % 10 == 0 and total // 10 == control
+
+
+def luhn_interactive():
+    """
+    This is command line interactive luhn checking algorithm.
+    User writes down a credit card and gets whether his card is correct or not.
+    """
+    while True:
+        try:
+            user_input = input("Write card number or -1 to quit: ")
+
+            if user_input == "-1":
+                break
+
+            if luhn_check(user_input):
+                print("Your card is correct.")
+            else:
+                print("Your card is incorrect.")
+        except EOFError:
+            break
+        except ValueError as e:
+            print(e)
+    print("Bye bye!")
+
+
+if __name__ == "__main__":
+    luhn_interactive()
diff --git a/test/test_fast_pow.py b/test/test_fast_pow.py
index 5e4aebd..1477329 100644
--- a/test/test_fast_pow.py
+++ b/test/test_fast_pow.py
@@ -1,9 +1,33 @@
-from src.fast_pow import fastPow
+from src.fast_pow import fast_pow
 
 
 def test_two_power_two():
-    assert fastPow(2, 2) == 4
+    assert fast_pow(2, 2) == 4
 
 
 def test_negative():
-    assert fastPow(-1, 4) == 1
+    assert fast_pow(-1, 4) == 1
+    assert fast_pow(-2, 3) == -8
+
+
+def test_negative_power():
+    epsilon = 1e-8
+
+    assert fast_pow(5, -1) - 0.2 <= epsilon
+    assert fast_pow(10, -2) - 0.01 <= epsilon
+    assert fast_pow(77, -5) - 77 ** (-5) <= epsilon
+
+    assert fast_pow(-0.2, -2) - 25 <= epsilon
+    assert fast_pow(-0.2, -1) - 5 <= epsilon
+
+
+def test_edge_cases():
+    assert fast_pow(1100101, 0) == 1
+    assert fast_pow(-13, 0) == 1
+    assert fast_pow(111, 0) == 1
+
+
+def test_roots():
+    assert fast_pow(9, 0.5) == 3
+    assert fast_pow(8, 1 / 3) == 2
+    assert fast_pow(64, 1 / 6) == 2
diff --git a/test/test_luhn.py b/test/test_luhn.py
index 1c021a2..a891878 100644
--- a/test/test_luhn.py
+++ b/test/test_luhn.py
@@ -1,9 +1,25 @@
-from src.luhn import luhnСheck
+import pytest
+
+from src.luhn import luhn_check
 
 
 def test_good():
-    assert luhnСheck("8571 2612 1234 5467")
+    assert luhn_check("8571 2612 1234 5466")
+    assert luhn_check("4  5  6  1     2  6  1  2     1  2  3  4     5  5  6  6")
 
 
 def test_bad():
-    assert not luhnСheck("4561 2612 1234 5463")
\ No newline at end of file
+    assert not luhn_check("4561 2612 1234 5463")
+    assert not luhn_check("4  5  6  1     2  6  1  2     1  2  3  4     5  4  6  4")
+    assert not luhn_check("4  5  6  1     2  6  1  2     1  2  3  4     5  4  6  7")
+
+
+def test_invalid():
+    with pytest.raises(ValueError):
+        luhn_check("abc")
+
+    with pytest.raises(ValueError):
+        luhn_check("451abc")
+
+    with pytest.raises(ValueError):
+        luhn_check("")