#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <algorithm>
#include <sstream>
#include <iostream>
#include <string>
#include <cstdio>
#include <cmath>

using namespace std;

int main() {

	long long N, dp[55];
	cin >> N;

	fill(dp,dp+N,-1);
	dp[0] = dp[1] = 1;

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

	cout<< dp[N] << endl;

	return 0;
}