#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, e) for (int i = (int)s; i < (int)e; ++i)
#define all(a) (a).begin(), (a).end()

int main() {
    cin.tie(nullptr);
    
    int N;
    cin >> N;
    N++;
    
    vector<ll> dp(N, 0);
    dp[0] = 1;
    
    rep(i, 1, N) {
        dp[i] += dp[i - 1];
        if (i != 1) dp[i] += dp[i - 2];
    }
    
    cout << dp[N - 1] << '\n';
}