instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
VTwtMVKmrRvL, WLoVtWtMVKmrDCke
answer:
tMVKmr


question:
RMurrwPjlfG, QBKrrwPDkTM
answer:
rrwP


question:
dmKobYfjsVxvxeSnubDsh, DdpDfjsVxvxeSnSyEbkhpGbf
answer:

fjsVxvxeSn