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

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    int n; cin >> n;
    vector<int64_t > a(n+1, 0);
    a[0] = 1;
    a[1] = 1;
    for (int64_t i = 2; i < n+1; i++) a[i] = a[i-1] + a[i-2];
    cout << a[n] << endl;
}