instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
lrBJDRkT, jmBJDrI
answer:
BJD


question:
haOsaSQcyodWhqQaC, BKLEUQcyodWhvVkmxBz
answer:
QcyodWh


question:
QGQZgEIClTQTjsXhbOO, OMyZgEIClTQWndkiVi
answer:

ZgEIClTQ