n=int(input())
original_list=[]
for x in range(n//6+1):
    for y in range(n//8+1):
        if n==6*x+8*y:
            original_list.append(x+y)
        else:
            pass
unique_list = list(set(original_list)) # 去除重复值
if unique_list:
    print(min(unique_list))
else:
    print(-1)