/*
Title: Staircase

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 method to count how many possible ways the child can run up to the stairs. You
need to return number of possible ways W.

Detailed explanation ( Input/output format, Notes, Images )
Input format :
Integer N

Output Format :
Integer W

Constraints :
1  n;
    output = Staircase(n);
    cout