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: qMnjlfIsQRtUlPggCpHqu, gfVndMwYDIsQRtUlPgqBJKCX
Example Output: IsQRtUlPg

Example Input: PTGjJWozVZfkwMrHdxg, SJNzfpYzVZfkwMrHZXEizGTe
Example Output:
zVZfkwMrH