instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
xtCJGe, DXCJSw
answer:
CJ


question:
TnbLNKnNSs, NhDLNKnNRd
answer:
LNKnN


question:
RwduMBkDazrwZP, UPzcwtWMBkDazrAw
answer:

MBkDazr