Climb the stairs - Problem

Problem1057--Climb the stairs

1057: Climb the stairs

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Time Limit : 1.000 sec Memory Limit : 128 MiB

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Description

Given a staircase with N steps, a child runs up the stair with either 1, 2 or 3 steps at a time. How many possible different ways for the child reach the Nth stair

Input

One integer N
$ 1 \leq N \leq 20 $

Output

One integer which is number of possible different ways

Sample Input Copy

Sample Output Copy

Source/Category

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