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

SOLUTION: NP

PROBLEM: nrIHKzJCdAQzUDRBYpg, JDzJCdAQzUMMYrLcfO

SOLUTION: zJCdAQzU

PROBLEM: PtCHgVApB, fVnHgVFk

SOLUTION:
HgV