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

Example Input: ZGkBNEDRAwURXnxBIOJkzTvg, HMAwURXnxBMfGbPOBf
Example Output: AwURXnxB

Example Input: FiKGCRXutEOzMqP, xdxRXutEsl
Example Output: RXutE

Example Input: aCzVXHcdJCfuuVWc, OalgVXHcdJCToPHi
Example Output:
VXHcdJC