//递推
#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	while(cin >> n){
		long long a[90];
		a[1] = 1;
		a[2] = 2;
		for(int i=3;i<=n;i++)
			a[i] = a[i-1] + a[i-2];
		cout << a[n] << endl;
	}	
	return 0;
}