#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int main() {
	ll N;
	cin >> N;
	ll dp[N + 1];
	dp[0] = 1, dp[1] = 1;
	for (ll i = 2; i <= N; i++) {
		dp[i] = dp[i - 1] + dp[i - 2];
	}
	cout << dp[N] << endl;
}