An urn contains a positive number of colored balls. You have no idea how many colors there are, but you do know that there are an equal number of balls of each color. You also know that adding 20 balls of a new color to the urn would not change the probability of drawing (without replacement) two balls of the same color. Before these extra balls are added, you decide to steal one ball from the urn. At this point, i.e. after your masterful theft of a ball and before 20 new ones are put in, how many balls are in the urn?