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

Example Input: vMYfFo, EHYfnP
Example Output: Yf

Example Input: inquDFuJxtBaaFGCaRzO, NYcnWDuDFuJxtBafxZWCUw
Example Output: uDFuJxtBa

Example Input: VzRWIgkMepWPeeak, lcIIbkMepWPmbKn
Example Output:
kMepWP