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

Example Input: TvNVpHLPYjBCeUpyxlzFZ, tgKdPKVYjBCeUpyPK
Example Output: YjBCeUpy

Example Input: lOedgdw, aoedgpn
Example Output: edg

Example Input: zsIfPkJNaNLuXyzHEuHKwl, biAgeVNaNLuXyzHERWZHvHnfbA
Example Output:
NaNLuXyzHE