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



int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    
    ll dp[n+1];
    dp[1] = 1;
    dp[2] = 2;
    
    for (int i = 3; i <= n; i++) {
        dp[i] = dp[i-1] + dp[i-2];
    }
    
    cout << dp[n] << endl;



    return 0;
}