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:
IGHhMfqLeBpnullsPInfBH, LTDBpnullsPIBynwCrCQ
answer:
BpnullsPI


question:
rorZoWuIzCPgBpvPx, vsQlBuIzCPgWgHKBk
answer:

uIzCPg