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

Example Input: KfjqnJLciTXqkJK, yqfRcfqnJLcisSB
Example Output: qnJLci

Example Input: BICndZkjoSidWivWATvtqsS, FzVWjoSidWivFaQhkRT
Example Output: joSidWiv

Example Input: lFDxpJlhL, iiDxpJlZj
Example Output:
DxpJl

