instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
XwBMFIV, SNLBMFZQ
answer:
BMF


question:
JAfPtjqqUYMD, cpXItjqqFN
answer:
tjqq


question:
IawXra, EUwXHZ
answer:

wX