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

Example Input: gWMyioGBRpwcXfr, AOQGBRpwcSccqBE
Example Output: GBRpwc

Example Input: aeQjEeiWGONmzGimhGiw, RIEeiWGONmOZuVYr
Example Output: EeiWGONm

Example Input: HhjbSgFhRJazXqk, UmDesjbSgFhRlCrN
Example Output:
jbSgFhR