instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
JXnHYuZvAYK, zhUYuZvASGhd
answer:
YuZvA


question:
jLbHvZmecfxMcGLXGVsO, erFBGmecfxMcJtDyKGZ
answer:
mecfxMc


question:
ztIBXCoSmfUNpZrrfX, EGwmfUNpZrrqOZ
answer:

mfUNpZrr