I am trying to get either of 2 specific villagers on a random Nook Mile Island in Animal Crossing. You get 1 villager on each island, each time you go there. On these islands, a potential villager is selected, out of a pool of 403. However, it can't be ones you already have, so for me, this means there are 397 possibilities. You also can't get duplicates, so if you see a villager, and don't recruit them, you won't see them again (no replacement). So each time there's a failure, the likelihood of getting one of the 2 villagers I want goes up. What's the expected number of trials before a 50% probability of success?