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

int main() {
    int n;
    cin >> n;
    long long int dp[60] = {};
    dp[0] = 1;
    for (int i = 0; i < n; ++i) {
        dp[i + 2] += dp[i], dp[i + 1] += dp[i];
    }
    cout << dp[n] << endl;
    return 0;
}