#include <iostream>

using namespace std;

unsigned long long x,f1,f2,f3,b;

int main()
{
    cin >> x;

    if(x == 1)
    {
        cout<<0;
        return 0;
    }

    else if(x == 2)
    {
        cout << 2;
        return 0;
    }

    f1 = 1;
    f2 = 1;
    b = 2;

    while(f1+f2 < x)
    {
        f3 = f1+f2;
        f1 = f2;
        f2 = f3;
        b++;
    }

    cout<<b;

    return 0;
}