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

Example Input: VRXUhOYfTul, JqZUhOYKq
Example Output: UhOY

Example Input: gWMyioGBRpwcXfr, AOQGBRpwcSccqBE
Example Output: GBRpwc

Example Input: pmvvZN, cevvGU
Example Output:
vv