instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
jLbHvZmecfxMcGLXGVsO, erFBGmecfxMcJtDyKGZ
answer:
mecfxMc


question:
KvPFobZEGs, eKFobZEtnm
answer:
FobZE


question:
reBOPVjV, lpBOPNU
answer:

BOP