Welcome to Cows and Bulls. This is a simple game in which you guess a number that I make up.
When you guess a number, I'll tell you how many cows and bulls you have. For every bull you have, you have a number in the right place; and for every cow you have, you have another number that matches, but is in the wrong place.
If the number is 12345 and you guess 54321, you will have one bull and four cows. If you then guess 12354, you'll get three bulls and two cows.