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

Example Input: DFRoMPNDAzNgtLsEPseOzC, qykyPjDAzNgtLsEPYTsNrJaNK
Example Output: DAzNgtLsEP

Example Input: rcKVmDzwJKeK, uYqmDzwJKxkGi
Example Output: mDzwJK

Example Input: URkNjyHVsUopeybZR, udPrqVsUopeybju
Example Output:
VsUopeyb