//
// Created by liuhuan on 18-10-29.
//
#include<bits/stdc++.h>

using namespace std;

int main() {
    int a[50], n;
    a[0] = a[1] = a[2] = 1;
    cin >> n;
    for (int i = 3; i < n; i++) {
        a[i] = a[i - 1] + a[i - 3];
    }
    cout << a[n - 1] << endl;
    return 0;
}