The Third Smallest Number

You are given $n$ distinct natural numbers $a_1, a_2, \dots, a_n$. By choosing two of them in order — that is, picking two distinct indices $i \ne j$, placing $a_i$ in front and $a_j$ behind — and concatenating them, you can form a new number.

For example, concatenating $3$ and $4$ gives $34$ or $43$. Likewise, for $a_1 = 1$ and $a_4 = 11$, the results $a_i a_j$ and $a_j a_i$ are counted as different results (because the concatenation order differs), even when their values coincide (both equal $111$ here).

List every number that can be formed this way in nondecreasing order, counting each equal value as many times as it occurs. Write a program that prints the third smallest number in this list.

The first line contains the count of numbers $n$ ($3 \le n \le 108$). Each of the next $n$ lines contains one $a_i$ ($1 \le a_i \le 10000$). The $n$ given numbers are all distinct.

Print the third smallest number on a single line.