instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
iUtNuU, iKtNWk
answer:
tN


question:
zRwQdelc, UdAUwQdejhe
answer:
wQde


question:
lkJcEaFyjCzCivaIabQlckAa, YUMZlaFyjCzCivaFiVXaqLbw
answer:

aFyjCzCiva