instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
bmsrkXGb, GcarkXOZF
answer:
rkX


question:
yywhNdZQkLSzbOvhluicHA, lfZQkLSzbOvhVC
answer:
ZQkLSzbOvh


question:
gcViSHuTuPsIHJntgkuVWlnU, xOuPsIHJntgxKbeRvV
answer:

uPsIHJntg