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# (.NET Core 3.1.201) (judge verdict: Accepted)

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

public class Contestant
{
    public static void Main(string[] args)
    {
        checked
        {
            var /*XN*/ (X, N) = (Int(), Int());
            var line = Console.ReadLine();
            var para = line == "" ? new HashSet<int>() :
            line.Split()
               .Select(int.Parse)
               .ToHashSet();

            for (int i = 0; ; i++)
            {
                var left = X - i;
                if (!para.Contains(left))
                {
                    Console.WriteLine(left);
                    return;
                }

                var right = X + i;
                if (!para.Contains(right))
                {
                    Console.WriteLine(right);
                    return;
                }
            }
        }
    }

    private static string NextInput = "";

    private static int Int() => int.Parse(Str());
    private static long Long() => long.Parse(Str());
    private static float Float() => float.Parse(Str());
    private static double Double() => double.Parse(Str());
    private static string Str()
    {
        var s = NextInput;
        if (s == "") s = Console.ReadLine();

        var idx = s.IndexOf(' ');
        if (idx >= 0)
        {
            NextInput = s.Substring(idx + 1);
            return s.Substring(0, idx);
        }
        NextInput = "";
        return s;
    }
}