instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
faHRBWyXsYzYmHQyy, aHTyXsYzYeXBFV
answer:
yXsYzY


question:
atDgsOWuP, UJMgsOrwj
answer:
gsO


question:
gXXKLNWsAcVpW, vtYNWsActGlRb
answer:

NWsAc