Game of Cards

Problem description: Sonu got bored of playing Solitaire all day, and has invented a new game of cards that he can play by himself. He takes a shuffled deck of cards with R red cards and B black cards. In each turn, Sonu draws a card. A red card awards him with -r points, while a black card awards him with +b points. He can stop drawing cards at any point he wishes. Sonu believes there must be a