In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.

Example Input: WTnsmP, INnsIM
Example Output: ns

Example Input: yRhCObvPZYoKUoQnyaatR, NHzLJYPZYoKUoQnJnIsZxC
Example Output: PZYoKUoQn

Example Input: NQRyMjVqbyY, uKYhMjVqzgj
Example Output:
MjVq