#include <bits/stdc++.h>
using namespace std;
int fibonacci(int v) {
    if (v == 0) {
        return 0;
    }
    if (v == 1) {
        return 1;
    }
    return fibonacci(v - 1) + fibonacci(v - 2);
}

int main() {
    int n; cin >> n;
    cout << 2 * fibonacci(n);
}

Solved.. I should not have used recursion