#include <iostream>
#include <vector>

using namespace std;

int main() {
    int fib_1 = 1, fib_2 = 1, ind = 2, A;
    cin >> A;
    while (fib_2 < A) {
        int tmp = fib_2;
        fib_2 += fib_1;
        fib_1 = tmp;
        ind++;
    }
    if (fib_2 == A)
        cout << ind;
    else
        cout << -1;
    system("pause");
}