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

Ex Input:
YRNpKFPGzUsgCOBJgbVG, TdEpMngFPGzUsgCOZykYRrLp

Ex Output:
FPGzUsgCO


Ex Input:
HLtkkRnWkgIdqbQH, dWeFUtkkRnWkgIdZhlQh

Ex Output:
tkkRnWkgId


Ex Input:
NlELRp, zbELQX

Ex Output:

EL