class Solution97

{

    //Function to count the number of ways in which frog can reach the top.

    static long countWays(int n){

        if(n==1) return 1L;

        if(n==2) return 2L;

        long p1=1L, p2=2L, p3=4L, tmp, mod=(long)(1e9 + 7);

        for(int i=4; i<=n; i++) {

            tmp = p3;

            p3 = (p1 + p2 + p3)%mod;

            p1 = p2;

            p2 = tmp;

        }

        return p3%mod;

    }

​

}