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

Example Input: nYoRQU, gQoRZQ
Example Output: oR

Example Input: zqRbqwgmqGIAGTeeoGFOSr, RFnLqwgmqGIAGLcEvAWxY
Example Output: qwgmqGIAG

Example Input: VzfojpOFNVduTnBMFaht, ZtTqgFNVduTnzIsCoCw
Example Output:
FNVduTn