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: Wrong Answer)

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

namespace AtCoder.ABC170
{
    public class Problem3
    {
        public static void Main(string[] args)
        {
            var a = Console.ReadLine().Split(" ");

            var X = int.Parse(a[0]);

            var N = int.Parse(a[1]);

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

            if (N == 100)
            {
                Console.WriteLine("0");
                return;
            }

            var bs = Console.ReadLine().Split(" ");

            var ps = new List<int>();

            foreach(var b in bs)
            {
                ps.Add(int.Parse(b));
            }

            var os = new List<int>();
            
            for(var i = 0; i < 100; i++)
            {
                if (!ps.Contains(i + 1))
                {
                    os.Add(i + 1) ;
                }
            }

            var diffs = new List<List<int>>();

            foreach (var o in os.OrderBy(x => x))
            {
                var diff = Math.Abs(X - o);
                var index = os.IndexOf(o);
                var d = new List<int> { diff, index };
                diffs.Add(d);
            }

            var idx = diffs.OrderBy(x => x[0]).ThenBy(x => x[1]).FirstOrDefault()[1];

            var answer = os[idx];

            Console.WriteLine(answer.ToString());
        }
    }
}