CF870A Search for Pretty Integers

You are given two lists of non-zero digits. Let's call an integer pretty if its (base $ 10 $ ) representation has at least one digit from the first list and at least one digit from the second list. What is the smallest positive pretty integer?

The first line contains two integers $ n $ and $ m $ ( $ 1

Print the smallest pretty integer.

In the first example $ 25 $ , $ 46 $ , $ 24567 $ are pretty, as well as many other integers. The smallest among them is $ 25 $ . $ 42 $ and $ 24 $ are not pretty because they don't have digits from the second list. In the second example all integers that have at least one digit different from $ 9 $ are pretty. It's obvious that the smallest among them is $ 1 $ , because it's the smallest positive integer.