instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
yiKkIxbKvNk, znaIxbKggg
answer:
IxbK


question:
jLbHvZmecfxMcGLXGVsO, erFBGmecfxMcJtDyKGZ
answer:
mecfxMc


question:
CUVDtyttGTXvjCjeZT, uaJtyttGTXvjuf
answer:

tyttGTXvj