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

Example Input: HHJAHyvNCGmJEljWrjvHOqf, msPVEbNCGmJEljsKRX
Example Output: NCGmJElj

Example Input: eFUexDIFlaPDUwrOb, mTvkKGUxDIFlaPDUwxGVpnIwbi
Example Output: xDIFlaPDUw

Example Input: QWvqbMjlycuEhwJv, zpUMjlycuEhwtfU
Example Output:
MjlycuEhw