The cunning liar went to the store and bought something worth 9 yuan with a face value of 100 yuan. The salesperson asked him for 91 yuan. So how much money did he cheat the store?
狡猾的骗子到商店用面值为100元的钞票买了9元的东西，售货员找他91元，这时，他又用自己已有的零钱给了9元钱，要回了自己的100元，那么他骗了商店多少元．
<result>91</result>