instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
bOvlVNWf, iivlVzWt
answer:
vlV


question:
UmYbssMbmsXkKQuzNasLOib, EMqlbmsXkKQuzNcyHrpZXOQW
answer:
bmsXkKQuzN


question:
yseftopxWDPo, fNZftopxWDpa
answer:

ftopxWD