instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
CkZOSZevST, bbZOSZIg
answer:
ZOSZ


question:
OyrqfQQnzOFUzrkDM, iBkQQnzOFewhjvO
answer:
QQnzOF


question:
YpejzF, xhejaW
answer:

ej