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

typedef long long ll;

int main() {
	int N;
	cin >> N;
	vector<ll> dp(N+1);
	dp[0]=1; dp[1]=1;
	for (int i = 1; i < N; i++) {
		dp[i+1] = dp[i] + dp[i-1];
	}
	cout << dp[N] << endl;
}