On a remote island lives a happy tribe. The island is so small that everybody knows everybody. The inhabitants are extremely intelligent and rational, except for the following: It is considered to be a big shame to have blue eyes. If one inhabitant discovers having blue eyes, he/she will flee from the island at midnight and never come back. Luckily there are no mirrors on the island, nobody knows genetics and everybody is too polite to talk about anybody's color of eyes. One day a missionary comes to the island. As he is about to leave he tells everybody that he finds it strange that there are two colors of eyes in such a small community, blue and brown. On the 43rd night after this happens, many inhabitants flee from the island. How many persons were blue-eyed on the island?