规则Rules：
标准数独基础上，圆圈内数字等于每条线上数字乘积的末位数。
Classic rules applied. Additionally, numbers in circle is the last digit of the product of the numbers on each line.
◆在线涂鸦 Draw it Online
◆在线做 Do it by CTC
◆在线做 Do it by Penpa
