Problems > Walks on a Star

Walks on a Star

Difficulty: 1800 4000 ms 128 MB

graphs matrix-exponentiation

Count the closed walks of length N that start and end at vertex 1 in a star with center 1 and leaves 2,3,4,5, modulo 109+7.

Input: one integer N.

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

Constraints:

  • 0 ≤ N ≤ 1018

Sample Tests

Input 1
2
Output 1
4
Input 2
0
Output 2
1

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