Father and mother do morning exercises, father can run around the playground in 4 minutes, mother can run in 5 minutes. If they start at the same time, what is the minimum number of minutes before they can meet at the start?
爸爸和妈妈进行晨练，爸爸4分钟可以绕操场跑一圈，妈妈5分钟可以跑一圈．如果他们同时起跑，至少多少分钟后可以在起点相遇？
<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<result>20</result>