The story says that when John, who invented a chess, introduced the game to his king, the king asked him to mention what salary he wanted for the invention. John asked the king to put one rice on the first box on the chess board, two on the next, four at the second next, and until there was rice on all the fields. The king said he would gladly do it, but soon changed his mind and decided to kill John. How much amount of rice did John ask for? Return the amount to a suitable weight unit (one gram contains about 64 rice). Why did the king change his mind?