#include <iostream>
#include <vector>
using namespace std;

int main()
{   unsigned long long  n,a,b,c,i=2;
    cin >> n; if(n<=1)
        {cout << 0;
        return 0;}
    a=1;b=1;
    while(1)
        {c=b;
        b+=a;
        a=c;
        if(b>=n)
            {cout << i;
            return 0;
            }
        i++;
        }
    return 0;
}