instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
cvZfWOwa, xOfWOhZs
answer:
fWO


question:
fBpRXPkikQokGVeS, FwUbKXkikQokGos
answer:
kikQokG


question:
fCrNUhpRkvnw, QQQzBNUhpRkeaOT
answer:

NUhpRk