#include <iostream>

int beolvas(std::istream &in) {
    int n;
    in >> n;

    return n;
}

int jarda(int n) {
    int t2 = 1, t1 = 1, h1 = 0;
    for (auto i = 2; i <= n; i++) {
        const auto t0 = t2 + t1 + h1;
        const auto h0 = 2 * t2 + h1;
        t2 = t1;
        t1 = t0;
        h1 = h0;
    }

    return t1;
}

void feldolgoz(int n) {
    std::cout << jarda(n) << std::endl;
}

int main() {
    const auto n = beolvas(std::cin);
    feldolgoz(n);

    return 0;
}