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

namespace AtCoder.XXX.C
{ 
    public class Program
    {
        public static void Main(string[] args)
        {
            var datas = cr();
            var x = datas[0];
            var n = datas[1];
            if(n == 0)
			{
                P(x);
                return;
			}
            var a = cr().ToList();
            var min = x;
            var max = x;
            while(true)
			{
                if(a.Contains(min))
				{
                    min--;
				}
				else
				{
                    //if(min >= 1)
					{
                        P(min);
                        return;
                    }   
				}
                if(a.Contains(max))
				{
                    max++;
				}
				else
				{
                   // if(max <= 100)
					{
                        P(max);
                        return;
                    }
				}
			}

        }

        private static StreamReader sr;
        public static int[] Ecr()
        {
            if (sr == null)
            {
                sr = new StreamReader("input.txt", Encoding.GetEncoding("UTF-8"));
            }
            return sr.ReadLine().Split().Select(int.Parse).ToArray();
        }
        public static  int[] cr()
        {
            return Console.ReadLine().Split().Select(int.Parse).ToArray();
        }
        public static string Er()
        {
            if (sr == null)
            {
                sr = new StreamReader("input.txt", Encoding.GetEncoding("UTF-8"));
            }
            return sr.ReadLine();
        }
        public static string r()
        {
            return Console.ReadLine();
        }
        public static int cri()
        {
            return int.Parse(Console.ReadLine());
        }
        public static void P(string str)
        {
            Console.WriteLine(str);
        }
        public static void P(int num)
        {
            P(num.ToString());
        }
    }
}