There is a vegetable greenhouse covered with plastic film, the length is 50 meters, and the cross section is a semicircle with a radius of 5 meters. How many square meters of plastic film should be used for this vegetable greenhouse?
有一个塑料薄膜覆盖的蔬菜大棚，长50米，横截面是一个半径为5米的半圆，这个蔬菜大棚至少用多少平方米的塑料薄膜？
<gadget id="calculator">1_570 + 78.5</gadget>
<output>1_648.5</output>

<result>1_648.5</result>