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

Ex Input:
jXbgnl, lUbglP

Ex Output:
bg

Ex Input:
ylyLVUjsmMrXMFAPDGIZsHq, cYymMrXMFAPjm

Ex Output:
mMrXMFAP

Ex Input:
VSAYoEsLeQrlsYUIAAn, niaEwQxLeQrlsYUEiov

Ex Output:
LeQrlsYU