Given $N$ strings of lowercase letters, compute the lexicographically largest string that is a subsequence of all $N$ strings.

String $s$ is a subsequence of string $t$ if $s$ can be obtained by deleting some of the letters in $t$. It is not required to delete any letters.

String $s$ is lexicographically larger than $t$ if $t$ is a prefix of $s$ or, given that index $i$ is the first mismatch in strings $s$ and $t$, the $i$th character of $s$ is larger than the $i$th character of $t$.

Constraints

$1\le N\le {10}^5$

The sum of the lengths of all strings will be at most ${10}^6$.

All strings will only contain lowercase letters.

Input Specification

The first line contains a single positive integer, $N$.

The next $N$ lines each contain a string of lowercase letters. The string is guaranteed to contain at least one letter.

Output Specification

Output the lexicographically largest common subsequence. If no nonempty subsequence exists, output -1.

Sample Input 1

2
quantum
xyene

Sample Output 1

n

Sample Input 2

1
cba

Sample Output 2

cba

Sample Input 3

3
a
ab
c

Sample Output 3

-1