instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
atDgsOWuP, UJMgsOrwj
answer:
gsO


question:
PnRypl, HvRydi
answer:
Ry


question:
VdQsLhlfdhYhldRzfFcud, uoVtfdhYhldaNpL
answer:

fdhYhld