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

Example Input: dsngGP, KvnglB
Example Output: ng

Example Input: QKlzsmHyBcC, snPtzsmHdMIv
Example Output: zsmH

Example Input: mVYfxw, wEYfCG
Example Output:
Yf