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

SOLUTION: fkmX

PROBLEM: jXbgnl, lUbglP

SOLUTION: bg

PROBLEM: BRfIswUAsquZMLt, WoEawUAsquZTncbtQu

SOLUTION:
wUAsquZ