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

[Q]: HXYkGv, GCYksu
[A]: Yk

[Q]: XbjDHRCWxdPbhibUKn, SrpuPDHRCWxdPbKPWEXNWbZ
[A]: DHRCWxdPb

[Q]: eYSgLF, FxSgfT
[A]:
Sg