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

Example Input: kWTQrtCaoTbXIiXDphMG, pLhxkfeDoTbXIiXDpCCzTYyZv
Example Output: oTbXIiXDp

Example Input: tmBlKUto, eFDBlKLy
Example Output: BlK

Example Input: yglMPLGgCnVnzTclyRYt, coBPNkdGLGgCnVnzTcDULiLl
Example Output:
LGgCnVnzTc