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

Example Input: yOGvgtAmwMwcIRtJ, cQtAmwMwcIRjfjO
Example Output: tAmwMwcIR

Example Input: OyrqfQQnzOFUzrkDM, iBkQQnzOFewhjvO
Example Output: QQnzOF

Example Input: OwxcIwDS, GECcIwPa
Example Output:
cIw