In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.

Ex Input:
XWKEpwGRkfCFZGOyZQOoypx, lhQkmVqeRkfCFZGOyugPLqs

Ex Output:
RkfCFZGOy


Ex Input:
goyZUz, QryZlD

Ex Output:
yZ


Ex Input:
qfkRpbDvnxHTixApVq, ZHKxDyDvnxHTHLpyW

Ex Output:

DvnxHT