Climbing Stairs (1,2,3)
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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