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

[EX Q]: BUvWkxrAvDQG, rHrkxrAkCE
[EX A]: kxrA

[EX Q]: oKZCAErEMqzODnkcNqxVdoBOC, yHzRJuSqzODnkcNqxExr
[EX A]: qzODnkcNqx

[EX Q]: GalfvOLHWyoWnRkQ, ddwKvOLHWyoXQaNbX
[EX A]:
vOLHWyo