It takes 5 people and 5 days to complete a project. After 5 people work for one day, one person will be transferred, and the remaining work will be completed by 4 people. How many days will it take to complete the project?
一项工程需要5人5天完成，5人工作一天后调走一人，剩下的工作由4人完成，问完成这项工程需要多少天？
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 + 1</gadget>
<output>6</output>

<result>6</result>