There were 843 tourists in the science and technology park in the morning, 265 people left at noon, and 409 people came in the afternoon. How many tourists were there in the park at this time?
科技园上午有游客843人，中午有265人离开，下午又来了409人，这时园内有多少位游客？
<gadget id="calculator">843 - 265</gadget>
<output>578</output>

<gadget id="calculator">578 + 409</gadget>
<output>987</output>

<result>987</result>