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

Example Input: WjyKtxKtEYjP, vuBZJZyKtxKtXRZs
Example Output: yKtxKt

Example Input: HiEuutntEBpU, fdkqEuutntEBABdGZRND
Example Output: EuutntEB

Example Input: cXuHtAytYoYnkNejgEckSA, RKpZreoDdYoYnkNejgEjfTtDBNPC
Example Output:
YoYnkNejgE