#include<bits/stdc++.h>
using namespace std;

typedef long long ll;
ll f[52];

int main() {
	int n; cin >> n;
	f[1] = 1;
	f[2] = 2;
	for (int i = 3; i <= n; i++) {
		f[i] = f[i - 1] + f[i - 2]; 
	}
	cout << f[n];
	return 0;
}