#include <bits/stdc++.h>

using namespace std;
using ll = long long;

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

    ll n;
    cin >> n;
    vector<ll> a(n+1);
    a[0] = 1;
    for (int i=0; i<n; i++){
        if (i+1<=n) a[i+1] += a[i];
        if (i+2<=n) a[i+2] += a[i];
    }

    cout << a[n] << endl;

    return 0;
}