#include <iostream>
#include <iomanip>
#include <sstream>
#include <string>
#include <cmath>
#include <iostream>
using namespace std;

int main() {
	int N;
	cin >> N;
	long long pat[51];

	pat[0] = 1;
	pat[1] = 1;

	for (int i = 2; i <= N;i++){
		pat[i] = pat[i-1] + pat[i-2];
	}
	cout << fixed << pat[N] << endl;
	return 0;
}