#include <iostream>

using namespace std;

int main() {
	long long int count[55];
	int n;
	cin >> n;
	count[0] = count[1] = 1;
	for (int i = 2; i <= n; i++)count[i] = count[i - 1] + count[i - 2];
	cout << count[n] << endl;
	return 0;
}