import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;
/*
* 度度熊想去商场买一顶帽子,商场里有N顶帽子,有些帽子的价格可能相同。度度熊想买一顶价格第三便宜的帽子,问第三便宜的帽子价格是多少?
*/
public class Baidu_thirdcost
{
public static void main(String[] args)
{
List<Integer> price = new ArrayList<Integer>();
// 首先输入一个正整数N(N <= 50),接下来输入N个数表示每顶帽子的价格(价格均是正整数,且小于等于1000)
Scanner sc = new Scanner(System.in);
while (sc.hasNext())
{
int N = sc.nextInt();
int[] cost = new int[N];
for (int i = 0; i < N; i++)
{
cost[i] = sc.nextInt();
if (!price.contains(cost[i]))
price.add(cost[i]);
}
Collections.sort(price);
if (price == null || price.size() < 3)
System.out.println(-1);
else
System.out.println(price.get(2));
}
}
}