diff --git a/hard/day_13/problem.txt b/hard/day_13/problem.txt
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+Bluemin is engaged in a game with red and blue marbles. He has arranged n marbles in a row from left to right. 
+Surprisingly, the arrangement forms a zebroid.
+
+A zebroid is a non-empty sequence of red and blue marbles where the colors alternate. 
+For instance, sequences like (red; blue; red) and (blue) are zebroids, while (red; red) is not.
+
+Now Bluemin ponders over the number of ways to select a zebroid subsequence from this arrangement. 
+He seeks your assistance in solving this intriguing puzzle and finding the count modulo 1000000007 (10^9 + 7).
+
+Input
+
+The first line presents a single integer n (1 ≤ n ≤ 10^6), indicating the count of marbles in Bluemin's sequence.
+
+Output
+
+Your task is to print a single number, the answer to the problem modulo 1000000007 (10^9 + 7).
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diff --git a/hard/day_13/solution.cpp b/hard/day_13/solution.cpp
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+//write your code here
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diff --git a/hard/day_13/solution_test_cases.txt b/hard/day_13/solution_test_cases.txt
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+Examples
+
+Input
+3
+Output
+6
+
+Input
+4
+Output
+11
+
+Note:
+Let's consider the first test sample. Let's assume that Bluemin initially had sequence (red; blue; red), so there are six ways to pick a zebroid:
+
+    pick the first marble;
+    pick the second marble;
+    pick the third marble;
+    pick the first and second marbles;
+    pick the second and third marbles;
+    pick the first, second and third marbles. 
+
+It can be proven that if Bluemin picks (blue; red; blue) as the initial sequence, the number of ways won't change.
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