#include<bits/stdc++.h>
using namespace std;
long long f[5005],n;
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];
	}
    if(n==0) cout<<0;
	else cout << f[n];
}