#include <iostream>
#define LL long long
using namespace std;

LL last2, last1, act, n, cnt;

int main()
{
    cin >> n;

    last2 = last1 = act = 1;

    if(n == 1)
        cout << 2;

    else
    {
        cnt = 2;

        while(act < n)
        {
            last2 = last1;
            last1 = act;
            act = last1 + last2;
            cnt++;
        }

        cout << cnt - 1;
    }
}