OddNumber

using System;



class OddNumber
{
    static void Main()
    {
        int numbers = int.Parse(Console.ReadLine());
        int values = 0;
        int count = 0;
        int[] positive = new int[20000000];
        int[] negative = new int[20000000];

        for (int i = 0; i < numbers; i++)
        {
            values = int.Parse(Console.ReadLine());
            if (values >= 0) { positive[values]++; }
            else { values = values * (-1); negative[values]++; }
        }

        for (count = 0; count < 2000000; count++)
        {
            if (positive[count] % 2 != 0)
            {
                Console.WriteLine(count);
                break;
            }
            if (negative[count] % 2 != 0)
            {
                Console.WriteLine(-count);
                break;
            }
        }
    }
}