#include "bits/stdc++.h"

using namespace std;
typedef long long ll;
const ll MOD = 1e9 + 7;
ll dp[51];
 int main() {
	 int N;
	 cin >> N;
	 dp[0] = dp[1] = 1;
	 for (int i = 2; i <= N; i++) dp[i] = dp[i - 1] + dp[i - 2];
	 cout << dp[N] << endl;
}