When Doudou calculates addition, he writes 9 by mistake in the ones digit of one addend, and writes 3 by mistake in the 8 in the hundreds digit of the other addition. The resulting sum is 637. What is the correct sum?
豆豆计算加法时，把一个加数个位上的6错写成9，把另一个加数百位上的8错写成3，所得的和是637，正确的和应该是多少？
<gadget id="calculator">637 - 3</gadget>
<output>634</output>

<gadget id="calculator">634 + 500</gadget>
<output>1_134</output>

<result>1_134</result>