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

int main() {
    int N; cin >> N;
    ll dp[N+1];
    dp[0] = 1;
    
    for (int i=1; i<=N; i++) {
        if (i==1) dp[i] = dp[i-1];
        else dp[i] = dp[i-1]+dp[i-2];
    }
    
    cout << dp[N] << endl;
}