In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
One example: PPdQTlHHTJEe, DydQTlHHVnmlLu
Solution is here: dQTlHH
Explanation: Here, 'dQTlHH' is the longest common substring in both the input strings 'PPdQTlHHTJEe' and 'DydQTlHHVnmlLu'.

Now, solve this: biiwpi, Zwiwaj
Solution:
iw