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.Linq;
using System.Security;
using System.Text;
using System.Threading.Tasks;

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var line1 = Console.ReadLine();
            var firstLine = line1.Split();

            bool tof = true;
            int answer = 0;
            int N = int.Parse(firstLine[0]);
            int count = 1;

            string[] secondLine = new string[int.Parse(firstLine[1])];

            if(firstLine[1] == "0")
            {
                tof = false;
            }
            else
            {
                var line2 = Console.ReadLine();
                secondLine = line2.Split();
                Array.Sort(secondLine);

                if (Method(secondLine, firstLine[0]) == -1)
                {
                    answer = int.Parse(firstLine[0]);
                }
                else
                {
                    while (tof)
                    {
                        if (Method(secondLine, $"{N - count}") == -1)
                        {
                            answer = N - count;
                            break;
                        }
                        else
                        {
                            N -= count;
                            count++;
                            count *= -1;
                            continue;
                        }
                    }
                }
            }
            Console.WriteLine(answer); 
        }

        public static int Method(string[] line, string str)
        {
            return Array.IndexOf(line, str);
        }
    }
}