Xiao Li is the owner of a store. A customer came here and bought a pair of shoes. The purchase price was 20 yuan, and the current price was 30 yuan. I found the customer 20 yuan, and later the neighbor found that the 50 yuan was a counterfeit bill. Xiao Li had to pay the neighbor 50 yuan. How much did Xiao Li lose in total?
小李是一家商店的店主，一位顾客来到这里买了一双鞋，进价20元，现价30元，顾客给了店主50元，小李没零钱，找邻居换了5张10元的，找了顾客20元，后来邻居发现50元是假钞，小李不得不赔邻居50元，问小李一共亏了多少元？
<gadget id="calculator">20 + 20</gadget>
<output>40</output>

<result>40</result>