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

Example Input: CxosNa, ikosdx
Example Output: os

Example Input: QgkpBHsrfRYJCa, AdjbKLpBHsrfbpBC
Example Output: pBHsrf

Example Input: sGrHRmELarByxp, cDCUnmELarBXbEfM
Example Output:
mELarB