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

xfZYYDKEqoRRu, ztCeYYDKEqoPG
YYDKEqo

gWMyioGBRpwcXfr, AOQGBRpwcSccqBE
GBRpwc

AfKRtVyyy, fjFeRtVytU

RtVy