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

Example Input: skZGHS, HsZGge
Example Output: ZG

Example Input: pqFpUjQGiofBOjfYkRW, pQMnCFlhFpUjQGiofbc
Example Output: FpUjQGiof

Example Input: PFwTaaRRhYfhDyaB, FBaaRRhYfhcSlyMYBF
Example Output:
aaRRhYfh