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

Example Input: yhhzISsXKEbA, KlPrazISsXKzmrVBG
Example Output: zISsXK

Example Input: uDaqoOpUtLDdTGTO, ncIgBjDPqoOpUtLDdTNtiEyarDO
Example Output: qoOpUtLDdT

Example Input: GELGrKcHUS, gTGrKccqlA
Example Output:
GrKc