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

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N;
    cin >> N;
    vector<long long> dp(N + 1, 0);
    dp[0] = 1;
    dp[1] = 1;
    for (int n = 2; n <= N; ++n) dp[n] = dp[n - 2] + dp[n - 1];
    cout << dp[N] << endl;
    return 0;
}