instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
AuSFmN, crSFXM
answer:
SF


question:
WjyKtxKtEYjP, vuBZJZyKtxKtXRZs
answer:
yKtxKt


question:
pSRDlRSRt, CXMDlRScrvI
answer:

DlRS