#include <stdio.h>

int main() {
    
    int n;
    scanf("%d",&n);

    int a = n % 8;
    int b = a % 6;

    int num;
    if(a == 0)
    {
        num = n / 8;
        printf("%d\n",num);
        return 0;
    }

    if((a != 0) && (b == 0))
    {
        num = ((n - a) / 8) +1;
        printf("%d\n",num);
        return 0;
    }

    if(a == 4)
    {
        num = n / 8 + 1;
        printf("%d\n",num);
        return 0;
    }
    if(a == 2)
    {
        num = n / 8 + 1;
        printf("%d\n",num);
        return 0;
    }
    printf("-1");
    return 0;
}