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: mjCEUoPmeKbvCgUtUL, SrHtrPmeKbvYpQAVp
Example Output: PmeKbv

Example Input: cBAvKWcnYzc, ANGvKWcUTt
Example Output:
vKWc