In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.

koIZvrJmfKCO, TBvrtjcWIZvrJmfKRZDOE
IZvrJmfK

jLbHvZmecfxMcGLXGVsO, erFBGmecfxMcJtDyKGZ
mecfxMc

yqpBNIVOEmeax, UGIVOEmDo

IVOEm