#include <iostream>
using namespace std;
#include <bits/stdc++.h>
int main() {
    int n;
    cin>>n;
    if(n%2==1)
    {
        cout<<-1<<endl;
    }
    else 
    {
    int result;
    int count6=0,count8=-1;
    int all6=n/6;
    int all8=n/8;
    int pause=0;
    for(int i=0;i<all6+1;i++)
    {
        for(int j=0;j<all8+1;j++)
        {
            if(6*i+8*j==n)
            {
                count6=i;
                count8=j;
                pause++;
                break;
            }
        }
        if(pause==1)
        {
            break;
        }
    }
    result=count6+count8;
    cout<<result<<endl;
    //cout<<count6<<" "<<count8;
    }
}
// 64 位输出请用 printf("%lld")