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

[EX Q]: QlJnxO, BLJnCQ
[EX A]: Jn

[EX Q]: RpaZAvSnEBgGapIPQgw, wcwYsXvSnEBgGapIwoIWROB
[EX A]: vSnEBgGapI

[EX Q]: mmlaFEqZXDbWX, nJIKaFEqZXQfujXI
[EX A]:
aFEqZX