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

SOLUTION: qnJLci

PROBLEM: gfXPLNzsyfEotmHL, oJeXPLNzsyJuXP

SOLUTION: XPLNzsy

PROBLEM: IdxlchtsEKHMsfCoeg, SZDqPVzDxlchtsEKfCHF

SOLUTION:
xlchtsEK