instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
fBpRXPkikQokGVeS, FwUbKXkikQokGos
answer:
kikQokG


question:
OXdSmcKG, XbDdSmJl
answer:
dSm


question:
zbSNNVc, agSNNtOQ
answer:

SNN