instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
mmDhYqPJC, qThYqxW
answer:
hYq


question:
IJQqdzqdaGEIcdyh, izlVdzqdaGGiPYz
answer:
dzqdaG


question:
pkYPfxHHY, vUPfxWQ
answer:

Pfx