Largest number

You are given $n$ non-negative integers. They are written one after another in some order to form a single number. Find the largest number that can be formed.

The first line contains $n$ ($1 \le n \le 10^5$). The second line contains $n$ integers ($0 \le a_i \le 10^9$).

A single number — the largest result, without extra leading zeros.

Sorting by value is wrong: $[10, 2]$ needs 210, so $2$ goes first. Sorting the strings lexicographically is wrong too: for $[3, 30]$ 330 > 303. The right comparator puts $a$ before $b$ if a + b > b + a (string concatenation). In the first example the answer is 9534330.

If all numbers are $0$, the answer is 0, not 000.

Source: UVa 10905.