#include <iostream>

using namespace std;

constexpr int N = 20;

int n;
int f[N];

int main() {
    cin >> n;
    f[0] = 1;
    f[1] = 1;

    for (int i = 2; i <= n; ++i) {
        f[i] += f[i - 1] + f[i - 2];
    }

    cout << f[n] << endl;

    return 0;
}