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.Globalization;
using System.Linq;

namespace AtCoder
{
    class Program
    {
        static void Main()
        {
            var input1 = Console.ReadLine().Split(" ");
            int x = int.Parse(input1[0]);
            int n = int.Parse(input1[1]);
            List<int> p = new List<int>();
            if (n > 0)
            {
                var input2 = Console.ReadLine().Split(" ");
                p = input2.Select(x => int.Parse(x)).ToList();
                p.Sort();
            }


            try
            {
                IEnumerator<(int, int)> pattern(int x)
                {
                    int count = 0;
                    while (true)
                    {
                        yield return (x - (count), (x + count));
                        if (count == x) yield break;
                        count++;
                    }
                }

                var pat = pattern(x);
                while (pat.MoveNext())
                {
                    if (!p.Contains(pat.Current.Item1))
                    {
                        Console.WriteLine(pat.Current.Item1);
                        return;
                    }

                    if (!p.Contains(pat.Current.Item2))
                    {
                        Console.WriteLine(pat.Current.Item2);
                        return;
                    }
                }
            }
            catch (Exception e)
            {
                Console.Write(e);
            }
        }
    }
}