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

Example Input: esIMEOgV, tNIMEybb
Example Output: IME

Example Input: SJIkEibGrqcrOBgGjYjJc, EervOGrqcrOBgGJZyx
Example Output: GrqcrOBgG

Example Input: rftjtGUobQyPr, hAsIcjtGUobQypxzCvw
Example Output:
jtGUobQy