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

SOLUTION: DWefw

PROBLEM: spGRUmIYuGl, qkqRUmItqU

SOLUTION: RUmI

PROBLEM: FREFxRKOPO, LswEFxRzjtm

SOLUTION:
EFxR