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: zmbmQuyNGOe, mUMEmQuyiuS
Example Output: mQuy

Example Input: AobSNopOqCgtbQvegFjmLJkKDV, uMGCgtbQvegFZN
Example Output:
CgtbQvegF