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

Example Input: UiaECWZf, gRyaECWLGRl
Example Output: aECW

Example Input: CkZOSZevST, bbZOSZIg
Example Output: ZOSZ

Example Input: RwKXVEIHHrsItlEClrPfz, WyCgqDBgHHrsItlECguIC
Example Output:
HHrsItlEC