500
An old king is dying, and wants to leave his kingdom to the wiser of his two sons. He tells them that he will hold a horserace, and the son whose horse is the last to reach the church and come back will inherit the realm. Immediately the younger son jumps on a horse and makes for the church at top speed. The king now knows that this is the wiser son, and leaves him the kingdom. Why?
The younger son jumped on the older son's horse. He realized that if they rode their own horses the race would never end.