instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
QeNePjbLBKbDOuAVTJtXL, xjPVOyPbLBKbDOuDsMSEF
answer:
bLBKbDOu


question:
yQRDycTycwH, ImycTycrR
answer:
ycTyc


question:
AhsuAHkvRUXqGnBqHIY, SnCeLzkgsuAHkvRUXqBXyj
answer:

suAHkvRUXq