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

Ex Input:
XeQwOS, OuQwNR

Ex Output:
Qw


Ex Input:
DGvUCrUVlUnQBShkWnfnceGasvI, NfzGUnQBShkWnpLMnY

Ex Output:
UnQBShkWn


Ex Input:
HhonwZSRfwiaybGBw, dYnwZSRfwqIL

Ex Output:

nwZSRfw