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: FSwxBJ, iTwxAa
Example Output: wx

Example Input: fBLKIgmIhdGqoVCFF, RiqSgmIhdGqoVvmwrsvZY
Example Output:
gmIhdGqoV