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

Example Input: aiqZheFuLtXAGRCGNBTAX, ssnVdztXAGRCGNBTIqmSJLZcy
Example Output: tXAGRCGNBT

Example Input: wNiHcaiUPHnjp, aSTmjcaiUPHFzOu
Example Output: caiUPH

Example Input: vpxaDUuuT, uxaLxaDUuKXnE
Example Output:
xaDUu