TASK DEFINITION: In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
PROBLEM: FgQsxN, UMQsIa

SOLUTION: Qs

PROBLEM: XEvxzelZaWRO, zXIelZaWBUn

SOLUTION: elZaW

PROBLEM: QxKlPeqkHjzIov, iTpUKPeqkHknUcW

SOLUTION:
PeqkH