#include <iostream>

using namespace std;
unsigned long long a,b,c,ord,x;
int main()
{
    cin>>x;
    a=1;b=1;ord=2;c=2;
    while(c<x)
    {
        b=a;a=c;
        c=a+b;
        ord++;
    }
    cout<<ord;
    return 0;
}