Ali loves to play Massive Multiplayer Online Role-playing Game (MMORPG), and he is very excited! The game uses a coin-based money system that can be acquired through playing in combat mode. After spending a long time playing in the combat mode to earn money. Ali meet a very generous user, EpicJohnny42. He made an offer to Ali: "if you give me all your money. I will give you double the amount". What Ali doesn't know is that EpicJohnny42 is a devious scammer. When they trade, EpicJohnny42 will give Ali double the amount, except he will "forget" to put the last digit