#include <bits/stdc++.h>
using namespace std;
int n;
long long f[5002];
int main(){
	cin >> n;
	f[1] = 1;
	f[2] = 2;
	for(int i = 3;i <= n;i++){
		f[i] = f[i - 1] + f[i - 2];
	}
	cout << f[n];
	return 0;
}