In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.

Example Input: wNiHcaiUPHnjp, aSTmjcaiUPHFzOu
Example Output: caiUPH

Example Input: DZfOjrQffR, CXOjrQQc
Example Output: OjrQ

Example Input: QYYNYVpVCJ, GgfjfZYNYVpVEhAa
Example Output:
YNYVpV