#include<iostream>
#include<vector>
using namespace std;
long long arr[51] = { 0 };

long long way(int n) {
	if (n == 1)return 1;
	if (n == 0)return 1;
	if (arr[n] != 0) {
		return arr[n];
	}
	arr[n]=way(n - 1) + way(n - 2);
	return arr[n];
}

int main() {
	int n = 0;
	cin >> n;
	cout << way(n) << endl;
	return 0;
}