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

Example Input: jkGcUm, dxGcSI
Example Output: Gc

Example Input: sEYtoQlG, XIstoQQPw
Example Output: toQ

Example Input: pqFpUjQGiofBOjfYkRW, pQMnCFlhFpUjQGiofbc
Example Output:
FpUjQGiof