diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..bebbbab
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,23 @@
+### VisualStudioCode ###
+.vscode/*
+!.vscode/settings.json
+!.vscode/tasks.json
+!.vscode/launch.json
+!.vscode/extensions.json
+!.vscode/*.code-snippets
+
+# Local History for Visual Studio Code
+.history/
+
+# Built Visual Studio Code Extensions
+*.vsix
+
+### VisualStudioCode Patch ###
+# Ignore all local history of files
+.history
+.ionide
+
+venv
+
+__pycache__
+.pytest_cache
diff --git a/.python-version b/.python-version
new file mode 100644
index 0000000..4c8b864
--- /dev/null
+++ b/.python-version
@@ -0,0 +1 @@
+3.12.3
\ No newline at end of file
diff --git a/src/bin_search.py b/src/bin_search.py
index 713abfc..3249226 100644
--- a/src/bin_search.py
+++ b/src/bin_search.py
@@ -1,6 +1,6 @@
-def binSearch(xs: list[int], x: int):
+def bin_search(xs: list[int], x: int):
     left, right = 0, len(xs) - 1
-    while left < right:
+    while left <= right:
         mid = (left + right) // 2
         if xs[mid] == x:
             return mid
diff --git a/src/checksum.py b/src/checksum.py
index 74b4fb0..6767de2 100644
--- a/src/checksum.py
+++ b/src/checksum.py
@@ -1,14 +1,31 @@
-def modulo11Checksum(ISBNNumber: str):
+def modulo_11_checksum(isbn_number: str):
+    digits = isbn_number.replace("-", "").replace(" ", "")
 
-    digits = [int(char) for char in ISBNNumber if char.isdigit()]
-
-    checkDigit = digits[-1]
+    if len(digits) != 10:
+        return False
 
     total = 0
-    for i in range(len(digits) - 1):
-        weight = 10
+    for i in range(10):
         digit = digits[i]
-        total += digit * weight
 
-    checksum = total + checkDigit
-    return checksum % 11 == 0
+        if digit.upper() == "X" and i == 9:
+            val = 10
+        elif digit.isdigit():
+            val = int(digit)
+        else:
+            return False
+        weight = 10 - i
+        total += val * weight
+
+    return total % 11 == 0
+
+
+if __name__ == "__main__":
+    while True:
+        isbn_string = input("Put number(-1 exit): ")
+        if isbn_string == "-1":
+            break
+        if modulo_11_checksum(isbn_string):
+            print("Correct")
+        else:
+            print("Incorrect")
diff --git a/test/test_bin_searh.py b/test/test_bin_searh.py
index d18d85b..e6d3a6d 100644
--- a/test/test_bin_searh.py
+++ b/test/test_bin_searh.py
@@ -1,13 +1,17 @@
-from src.bin_search import binSearch
+from src.bin_search import bin_search
 
 
 def test_middle():
-    assert binSearch([1, 2, 3, 4, 5], 4) == 3
+    assert bin_search([1, 2, 3, 4, 5], 4) == 3
 
 
 def test_start():
-    assert binSearch([1, 2, 3, 4], 2) == 1
+    assert bin_search([1, 2, 3, 4], 2) == 1
+
+
+def test_one_value():
+    assert bin_search([6], 6) == 0
 
 
 def test_not_in_list():
-    assert binSearch([1, 2, 3, 4], 5) == -1
+    assert bin_search([1, 2, 3, 4], 5) == -1
diff --git a/test/test_checksum.py b/test/test_checksum.py
index f64a64c..2c0c436 100644
--- a/test/test_checksum.py
+++ b/test/test_checksum.py
@@ -1,9 +1,13 @@
-from src.checksum import modulo11Checksum
+from src.checksum import modulo_11_checksum
 
 
 def test_good():
-    assert modulo11Checksum("2-266-11156-8")
+    assert modulo_11_checksum("0-306-40615-2")
+
+
+def test_whith_x():
+    assert modulo_11_checksum("0-8044-2957-X")
 
 
 def test_bad():
-    assert not modulo11Checksum("2-266-11156-3")
+    assert not modulo_11_checksum("2-266-11156-3")