In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
One example is below.
Q: PPdQTlHHTJEe, DydQTlHHVnmlLu
A: dQTlHH
Rationale: Here, 'dQTlHH' is the longest common substring in both the input strings 'PPdQTlHHTJEe' and 'DydQTlHHVnmlLu'.
Q: NqPHWyYS, PhPHWIaA
A:
PHW