#include <iostream>
#include <vector>
using namespace std;
int main(){
	int N;
	cin >> N;
	vector<long long> dp(N + 1);
	dp[0] = 1;
	dp[1] = 1;
	for (int i = 2; i <= N; i++){
		dp[i] = dp[i - 2] + dp[i - 1];
	}
	cout << dp[N] << endl;
}