instruction:
In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.
question:
IGHhMfqLeBpnullsPInfBH, LTDBpnullsPIBynwCrCQ
answer:
BpnullsPI


question:
HaIPcFXLhYDp, AdIPcFXtJdRE
answer:
IPcFX


question:
BmxgSFWBlVX, kGgKrgSFWBlGunFcZ
answer:

gSFWBl