#include<iostream>
using namespace std;
int main() {
	int F[45];
	F[0] = 1;
	F[1] = 1;
	int n;
	cin >> n;
	for (int i = 2; i <= n; i++) {
		F[i] = F[i - 1] + F[i - 2];
	}
	cout << F[n] << endl;
	return 0;
}