2 D

#include <iostream>
#include <vector>

using namespace std;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    long long n;
    cin >> n;
    vector<long long> v(2);
    v[0] = 0; v[1] = 1;

    if (n == 0) cout << 0;
    else if (n == 1) cout << 1;
    else {
        int it = 2;
        while (v.back() < n) {
            v.push_back(v[it - 1] + v[it - 2]);
            it++;
        }

        if (v.back() == n) cout << it - 1;
        else cout << -1;
    }

    return 0;
}