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

Example Input: QgkpBHsrfRYJCa, AdjbKLpBHsrfbpBC
Example Output: pBHsrf

Example Input: OezHeoe, ouUzHemU
Example Output: zHe

Example Input: qNFfFcXlWHbNasMSpnyz, OYXlWHbNasnnIWp
Example Output:
XlWHbNas