formula_recursiva_cuatro.cpp11

#include <iostream>

using namespace std;

int v[40] = {0};

int f(int n) {
    if(v[n]!=0) {
        return v[n];
    }
    if(n<=3) {
        return 1;
    }
    v[n] = f(n-1)+f(n-2)+f(n-3);
    return v[n];
}

int main() {
    int n;
    cin >> n;
    cout << f(n) << endl;
    cin.get();
    return 0;
}