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Competitions

# Grasshopper

Grasshopper lives in the teacher's room. It likes to jump on one dimensional checkerboard. The length of the board is n cells. To its regret, it can jump only on 1, 2, ..., k cells forward.

Once teachers wondered in how many ways a grasshopper can reach the last cell from the first one. Help them to answer this question.

#### Input

Two integers n and k (1n30, 1k10).

#### Output

Print the number of ways for grasshopper to leap from the first cell to the last.

Time limit 1 second
Memory limit 128 MiB
Input example #1
8 2

Output example #1
21

Input example #2
1 10

Output example #2
1

Input example #4
1 1

Output example #4
1