orange=int(input())
ji=orange//2
if orange%2==0:
    if ji%4==0:
        print(ji//4)
    else:
        print(ji//4+1)
    # elif ji%4==1:
    #     print(ji//4+1)
    # elif ji%4==2:
    #     print(ji//4+1)
    # elif ji%4==3:
    #     print(ji//4+1)
else:
    print(-1)