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

Example Input: HorIyjpfBFmKZQUIEoP, AcWOaOgVPmyjpfBFmKZQPFYiI
Example Output: yjpfBFmKZQ

Example Input: ICizmXnKMpUH, oDrnmXnKgWXX
Example Output: mXnK

Example Input: mvsTfMggfLtXGgI, okwtXTfMggfLejEp
Example Output:
TfMggfL