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

Example Input: pqFpUjQGiofBOjfYkRW, pQMnCFlhFpUjQGiofbc
Example Output: FpUjQGiof

Example Input: aZcGMvzBhazkCIFqpVe, AOljBvzBhazkWXeTuA
Example Output: vzBhazk

Example Input: MrfHssFwelrsSUIAlPffp, PwHcgyFFsFwelrsSUPpxnk
Example Output:
sFwelrsSU

