instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
LeHzcEFc, WFzcExvJ
answer:
zcE


question:
fVEFJa, WtEFYK
answer:
EF


question:
UGNzVlsjVFdYiwcGF, ilLVlsjVFdyTF
answer:

VlsjVFd