#include "bits/stdc++.h"
using namespace std;

int main() {
	long long N, DP[60] = {};
	cin >> N;
	DP[0] = 1, DP[1] = 1;
	for (int i = 2; i <= N; i++) DP[i] = DP[i - 1] + DP[i - 2];
	cout << DP[N] << endl;
}