There is a shopkeeper, Jack, who sells his goods for zero profit. One day a lady comes to him and buys some stuff for 20$. She hands Jack a 100$ note and Jack realizes that he doesn't has any change. So he goes to a fellow shopkeeper, Ron, and gets it. He returns the lady 80$ and keeps the remaining 20$. The lady leaves. After some time Ron comes to Jack and tells him that the 100$ note is fake. Jack returns him 100$. How much did Jack loose?