Problem Statement
As they say, small is cute and beautiful.

Given N distinct positive integers, find the smallest number that can be formed by concatenating all of them.
Input Format
The first line of the input file contains a positive integer N. Then N lines follow.
Each line contains a single positive integer K.

Output Format
Output the smallest possible number that can be formed by concatenating all the numbers.

Constraints
1 ≤ N ≤ 5000
1 ≤ K ≤ 10^15

SAMPLE INPUT
5
14
66
907
1234567890
9876543210

SAMPLE OUTPUT
123456789014669079876543210

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