There is a football made of 32 pieces of black and white cowhide stitched together. The black leather can be regarded as a regular pentagon, and the white leather can be regarded as a regular hexagon. Each piece of white leather has three sides sewn together with the black leather. How many pieces of black leather are there?
有一种足球是由32块黑白相间的牛皮缝合而成的，黑皮可看作正五边形，白皮可看作正六边形，每块白皮有三条边和黑皮缝在一起，则黑皮有多少块．
<gadget id="calculator">32 - 20</gadget>
<output>12</output>

<result>12</result>