An eight-digit number, the high digit is 7, the difference between any adjacent digits is 3, what is the lowest digit.
一个八位数，高位是7，任意相邻的数位上的数字相差3，最低位上是多少．
<gadget id="calculator">7 - 3 - 3</gadget>
<output>1</output>

<gadget id="calculator">3 - 3</gadget>
<output>0</output>

<gadget id="calculator">1 + 3 + 0</gadget>
<output>4</output>

<result>4</result>