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

Ex Input:
kWTQrtCaoTbXIiXDphMG, pLhxkfeDoTbXIiXDpCCzTYyZv

Ex Output:
oTbXIiXDp

Ex Input:
TWVTGNBh, nEVTGWq

Ex Output:
VTG

Ex Input:
ZGMHBeIrWgcfTQWTCl, gqNHBtGBeIrWgcfTQxad

Ex Output:
BeIrWgcfTQ