Challenge: Staircase Problem

Problem statement

A child is running up a staircase with n steps and can hop either 1 step, 2 steps, or 3 steps at a time. Implement a function to count the number of possible ways that the child can run up the stairs.

Input

An integer that represents the number of stairs

Output

An integer that represents the number of ways that those stairs can be climbed

Sample input

int n = 4;

Sample output

int n = 7;

Coding exercise

Take a close look and design a step-by-step algorithm before jumping to the implementation. This problem is designed for your practice, so try to solve it on your own first. If you get stuck, you can always refer to the hint and solution provided in the code tab. Good Luck!