instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
zgJGhxLU, EwJGhedW
answer:
JGh


question:
lsNwypFwhKP, diEfLwypFwEKqCN
answer:
wypFw


question:
xrDrnnkbABn, vmfnnkbHhhX
answer:

nnkb