numofway.cpp

#include<iostream>
#include<cstdlib>

#define long long long
#define nln '\n'

using namespace std;

long s, e;

long recursion(long i)
{
    if (i < s)
        return 0;
    if (i == s || i == s+1)
        return 1;
    if (i == s+2)
        return 2;
    if (i == s+3)
        return 4;
    return recursion(i-1)+recursion(i-2)+recursion(i-3);
}

int main()
{
    cin.tie(0)->sync_with_stdio(0);
    cout.tie(0)->sync_with_stdio(0);
    //freopen("numofway.inp", "r", stdin);
    cin >> s >> e;
    cout << recursion(e) << nln;
    return 0;
}