Statement

Given $$$n$$$ strings. Find the string $$$s$$$ with minimum length such that each of $$$n$$$ given strings is a substring of $$$s$$$.

Constraint

$$$n \le 50$$$

Every of $$$n$$$ strings has length not exceed $$$10$$$

Example:

Input:

3
ab
ba
abb

Output:

abba

This problem is hard for me. Can you give me a hint? Thank you in advance.