Closed Walks on Path of Four

Difficulty: 1800 4000 ms 128 MB

graphs matrix-exponentiation

Count the closed walks of length N starting and ending at vertex 1 in the graph Path of Four, modulo 10⁹+7.

Input: one integer N.

Output: the number of closed walks mod 10⁹+7.

Constraints:

• 0 ≤ N ≤ 10¹⁸

Sample Tests

2

1

0

1

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