Problem:
Score : 300 points

Problem Statement

Takahashi made N problems for competitive programming.
The problems are numbered 1 to N, and the difficulty of Problem i is represented as an integer d_i (the higher, the harder).

He is dividing the problems into two categories by choosing an integer K, as follows:

A problem with difficulty K or higher will be for ARCs.

A problem with difficulty lower than K will be for ABCs.

How many choices of the integer K make the number of problems for ARCs and the number of problems for ABCs the same?

Problem Statement

2 \leq N \leq 10^5

N is an even number.

1 \leq d_i \leq 10^5

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
d_1 d_2 ... d_N

Output

Print the number of choices of the integer K that make the number of problems for ARCs and the number of problems for ABCs the same.

Sample Input 1

6
9 1 4 4 6 7

Sample Output 1

2

If we choose K=5 or 6, Problem 1, 5, and 6 will be for ARCs, Problem 2, 3, and 4 will be for ABCs, and the objective is achieved.
Thus, the answer is 2.

Sample Input 2

8
9 1 14 5 5 4 4 14

Sample Output 2

0

There may be no choice of the integer K that make the number of problems for ARCs and the number of problems for ABCs the same.

Sample Input 3

14
99592 10342 29105 78532 83018 11639 92015 77204 30914 21912 34519 80835 100000 1

Sample Output 3

42685

Solution in C# (Mono 4.6.2.0) (judge verdict: Time Limit Exceeded)

using System;
using System.Collections.Generic;
using System.Linq;

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            int cnt = 0;
            var mondaisuu = int.Parse(Console.ReadLine());
            var mondai = Console.ReadLine().Split().Select(x => int.Parse(x)).OrderBy(x => x).ToList();
            var maxLevel = mondai.Max();

            for (int K = mondai[mondaisuu / 2 - 1]; K < maxLevel; K++)
            {
                var arcMondai = mondai.Where(x => x >= K);
                var abcMondai = mondai.Where(x => x < K);
                if (IsCountMatch(arcMondai, abcMondai))
                {
                    cnt = arcMondai.Min() - abcMondai.Max();
                    break;
                }
            }

            Console.WriteLine(cnt);
        }

        private static bool IsCountMatch(IEnumerable<int> mondaiA, IEnumerable<int> mondaiB)
        {
            return mondaiA.Count() == mondaiB.Count();
        }

    }
}