CF2010B Three Brothers

Three brothers agreed to meet. Let's number the brothers as follows: the oldest brother is number $ 1 $ , the middle brother is number $ 2 $ , and the youngest brother is number $ 3 $ . When it was time for the meeting, one of the brothers was late. Given the numbers of the two brothers who arrived on time, you need to determine the number of the brother who was late.

The first line of input contains two different integers $ a $ and $ b $ ( $ 1

Output a single integer — the number of the brother who was late to the meeting.