In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
Example: PPdQTlHHTJEe, DydQTlHHVnmlLu
Example solution: dQTlHH
Example explanation: Here, 'dQTlHH' is the longest common substring in both the input strings 'PPdQTlHHTJEe' and 'DydQTlHHVnmlLu'.

Problem: ELtaSfXJlEkuzyxw, XqfXJlEkigh

Solution: fXJlEk