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

Example Input: sCMyALRSDknURKqZDlqFf, oEIfHyALRSDknUrnMebev
Example Output: yALRSDknU

Example Input: wYhGWdRC, cFGWdHEy
Example Output: GWd

Example Input: KULgSG, pGLgLf
Example Output:
Lg