instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
nYoRQU, gQoRZQ
answer:
oR


question:
kOrQWjLKnwN, xFsWjLKgr
answer:
WjLK


question:
qtGtaYvsMIMoUhuiE, WcWOeEJGtaYvsMIMxRWo
answer:

GtaYvsMIM