#include <iostream>
using namespace std;

int main(){
	int n;

	while(cin >> n){
		
		long long a=1;
		long long b=2;
		
		if(n==1){
			cout << 1 << endl;
			continue;
		}
		
		if(n==2){
			cout << 2 << endl;
			continue;
		}
		
		long long c;
		for(int i=3;i<=n;i++){
			c = a+b;
			a = b;
			b = c;
		}
		cout << c << endl;
	}
	return 0;
}