#include <iostream>
using namespace std;

long long answer(long long n) {
    if (n == 1) {
        return 0;
    } else if (n == 2) {
        return 1;
    } else if (n == 3) {
        return 1;
    } else {
        return answer(n - 3) + 2 * answer(n - 2) + answer(n - 1);
    }
}

int main() {
    long long number;
    cin >> number;
    long long ans = answer(number);
    cout << ans << endl;
    return 0;
}
//这道题还行,1用递归还给了公式