Suppose that there is a collection of 3n distinct coupons, n of which are colored red and 2n of which are colored blue. Suppose that each time you go to a ticket window to get a coupon, the clerk first randomly decides, with probability 1/2, whether he will give you a red coupon or blue coupon and then he chooses a coupon uniformly at random from among the coupons that are that color. What is the expected number of times that you must visit the ticket window to get all 3n coupons?