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

Example Input: iupYjFXrrMqWzJSLUSwmEukHc, hqajjWrrMqWzJSLnF
Example Output: rrMqWzJSL

Example Input: jinzsW, SMnzaW
Example Output: nz

Example Input: RYnyOTGedjcKzbmavFsHYfX, UxuAGedjcKzbmLscnV
Example Output:
GedjcKzbm