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

Example Input: koIZvrJmfKCO, TBvrtjcWIZvrJmfKRZDOE
Example Output: IZvrJmfK

Example Input: bmZKWkYPqugcvzbHykblPzQLhK, tPUzKqugcvzbHypzk
Example Output: qugcvzbHy

Example Input: OYrrtqXcpVhsdMgzoDitt, dsBflTPwqXcpVhsdMEBjvE
Example Output:
qXcpVhsdM