#include <iostream>
using namespace std;

int main() {
    int n,m,s=0,i;
    cin>>n;
    for(i=n/8;i>=0;i--)
    {
        m=n-i*8;
        if(m%6==0)
        {
            s=m/6+i;
            break;
        }

    }
    if(i==-1)cout<<-1;
    else
    cout<<s;
}