instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
PGjDRPDzGaBR, rpIJRPDzWi
answer:
RPDz


question:
jFVaEHbMrrkW, ekfVaEHbPnBnM
answer:
VaEHb


question:
YmlXsLmSvDyxfh, QAElXsLmSABhs
answer:

lXsLmS