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

Example Input: RpaZAvSnEBgGapIPQgw, wcwYsXvSnEBgGapIwoIWROB
Example Output: vSnEBgGapI

Example Input: KfjqnJLciTXqkJK, yqfRcfqnJLcisSB
Example Output: qnJLci

Example Input: wJHqWwihTksnQVsPc, ixaiXxihTksnVbBbmw
Example Output:
ihTksn