#include <iostream>

using namespace std;

#define LL long long

int main()
{
	freopen ("nunta.in", "r", stdin);
	freopen ("nunta.out", "w", stdout);
	
	int N;
	
	scanf ("%d", &N);
	
	LL prez = 0, ant = 0, ult = 1;
	
	for (int i = 1; i <= N; ++ i)
	{
		prez = ant + ult;
		ant = ult;
		ult = prez;
	}
	
	printf ("%lld", ult);
	
	return 0;
}