instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
VByrCcgcxCfPGDFqIWGloQZTMQf, OqfPGDFqIWGlalTCCkKkMf
answer:
fPGDFqIWGl

question:
zeuyZKwvIOfx, BlmZKwvspUt
answer:
ZKwv

question:
zHTnUQgxyuWYK, EbuEQgxyufPF
answer:
Qgxyu