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