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

Example Input: pJqqIW, Ivqqxw
Example Output: qq

Example Input: ZyrpGdXvvtrKQIxU, CLNGdXvvtrKQDpicfqLdt
Example Output: GdXvvtrKQ

Example Input: OlVaooWhJMaGaOPKww, EmSxooWhJMaGzHjONK
Example Output:
ooWhJMaG