Ciel and A-B Problem

In Ciel's restaurant, a waiter is training. Since the waiter isn't good at arithmetic, sometimes he gives guests wrong change. Ciel gives him a simple problem. What is A-B (A minus B) ? Surprisingly, his answer is wrong. To be more precise, his answer has exactly one wrong digit. Can you imagine this? Can you make the same mistake in this problem? Input An input contains 2 integers A and B. Ou