#include <iostream>
using namespace std;

int main(void) {
    int N;
    cin >> N;
    long long masu[52] = {1};
    for (int i = 0; i < N; i++) {
        masu[i+1] += masu[i];
        masu[i+2] += masu[i];
    }
    cout << masu[N] << endl;
    return 0;
}