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

Example Input: xfZYYDKEqoRRu, ztCeYYDKEqoPG
Example Output: YYDKEqo

Example Input: SyweIt, ILweip
Example Output: we

Example Input: cinkuLQnxhf, HguINkuLQnEpK
Example Output:
kuLQn