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


int main() {
    ios::sync_with_stdio(false);
    ll n;
    cin >> n;
    ll a[100];
    a[1] = 1;
    a[2] = 2;

    for (ll i = 3; i <= n; i++)
        a[i] = a[i-1] + a[i-2];
    
    cout << a[n] << endl;








    return 0;
}