#include <bits/stdc++.h>
using namespace std;
int putere2(long long x)
{
   while(x%2==0)
    x/=2;
    if(x==1)
        return 1;
    return 0;
}
int main()
{
long long n,nr=0,aux;
    cin>>n;
    aux=n;
    if(putere2(n))
    {
        while(aux!=1)
        {
            aux/=2;
            nr++;
        }
        cout<<nr;
    }
     else cout<<-1;
    return 0;
}