#include <iostream>
#include <math.h>
#include <string>
#include <algorithm>
using namespace std;

int main(){
	int n;
	cin >> n;
	long long a[51];
	a[0] = 1;
	a[1] = 1;
	for (int i = 2; i <= n; i++){
		a[i] = a[i - 1] + a[i - 2];
	}
	cout << a[n] << endl;
	return 0;
}