Problem:
Score : 300 points

Problem Statement

Given are an integer X and an integer sequence of length N: p_1, \ldots, p_N.

Among the integers not contained in the sequence p_1, \ldots, p_N (not necessarily positive), find the integer nearest to X, that is, find the integer whose absolute difference with X is the minimum. If there are multiple such integers, report the smallest such integer.

Constraints

1 \leq X \leq 100

0 \leq N \leq 100

1 \leq p_i \leq 100

p_1, \ldots, p_N are all distinct.

All values in input are integers.

Input

Input is given from Standard Input in the following format:

X N
p_1 ... p_N

Output

Print the answer.

Sample Input 1

6 5
4 7 10 6 5

Sample Output 1

8

Among the integers not contained in the sequence 4, 7, 10, 6, 5, the one nearest to 6 is 8.

Sample Input 2

10 5
4 7 10 6 5

Sample Output 2

9

Among the integers not contained in the sequence 4, 7, 10, 6, 5, the ones nearest to 10 are 9 and 11. We should print the smaller one, 9.

Sample Input 3

100 0

Sample Output 3

100

When N = 0, the second line in the input will be empty. Also, as seen here, X itself can be the answer.

Solution in C# (Mono-mcs 6.8.0.105) (judge verdict: Wrong Answer)

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

namespace ABC170C
{
    class Program
    {
        static void Main(string[] args)
        {
            var XN = Console.ReadLine().Split().Select(int.Parse).ToArray();
            var X = XN[0];
            var N = XN[1];

            if (N == 0)
            {
                Console.WriteLine(X);
                return;
            }

            var pSet = new HashSet<int>(Console.ReadLine().Split().Select(int.Parse).OrderBy(x => x));

            if (pSet.Count == 100)
            {
                Console.WriteLine(0);
                return;
            }

            var a = 0;
            for (var i = X; i <= 101; i++)
            {
                if (!pSet.Contains(i))
                {
                    a = i;
                    break;
                }
            }

            var b = 0;
            for (var i = X; i >= 0; i--)
            {
                if (!pSet.Contains(i))
                {
                    b = i;
                    break;
                }
            }

            if (Math.Abs(X - a) < Math.Abs(X - b))
                Console.WriteLine(a);
            else
                Console.WriteLine(b);

        }
    }
}