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

Example Input: bUHPpvVtFQNSpUdg, zggEFoKBHPpvVtFQNHXsc
Example Output: HPpvVtFQN

Example Input: VGRjWGHRcBdFmkVg, eSwqALQXWGHRcBdFsDXCM
Example Output: WGHRcBdF

Example Input: wOKATs, NDKAep
Example Output:
KA