#include<bits/stdc++.h>
#define pii pair<int, int>
#define fi  first
#define se  second
#define ll  long long
#define pb  emplace_back

using namespace std;

const int N = 1e5+7;
ll n, f[57];

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(0); cout.tie(0);
	
	cin >> n;
	f[1] = 1;
	f[2] = 2;
	for(ll i = 3; i <= n; i++) f[i] = f[i-1] + f[i-2];
	cout << f[n];
	return 0;
}