#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
const int N = 1e6 + 10;
int n, x, y, z;
void solve() {
    cin >> n;
    x = y = z = 1;
    for (int i = 2; i <= n; i++) {
        z = x + y;
        x = y;
        y = z;
    }
    cout << z;
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    solve();
    return 0;
}