Cut two ribbons with lengths of 45 cm and 15 cm into short ribbons of the same length, and there is no surplus. What is the longest length of each string in centimeters?
把两根长度分别是45厘米和15厘米的彩带剪成长度一样的短彩带，并且没有剩余，每根绳子最长是多少厘米．
<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<result>15</result>