#include <iostream>

using lint = long long;

void solve() {
    int n;
    std::cin >> n;

    lint a = 0, b = 1;
    while (n--) {
        auto c = a + b;
        a = b;
        b = c;
    }

    std::cout << b << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}