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Problems > Climbing Stairs (1,2,3)

Climbing Stairs (1,2,3)

Difficulty: 1800 4000 ms 128 MB

dp matrix-exponentiation

Count the ways to climb a staircase of N steps taking 1, 2, or 3 steps at a time, modulo 109+7.

Input: one integer N.

Output: the number of ways mod 109+7.

Constraints:

  • 0 ≤ N ≤ 1018

Sample Tests

Input 1
0
Output 1
1
Input 2
3
Output 2
4
Input 3
4
Output 3
7

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