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.Generic;
using System.Linq;
using System.Text;
using System.IO;
class Program
{
    static void Main(string[] args)
    {
            // 入力
            string[] sS = System.Console.ReadLine().Trim().Split(' ');
            int iX = int.Parse(sS[0]);
            int iN = int.Parse(sS[1]);
            List<int> lstP = new List<int>();
            if (iN > 0)
            {
                sS = System.Console.ReadLine().Trim().Split(' ');
                for (int i = 0; i < sS.Length; i++)
                {
                    lstP.Add(int.Parse(sS[i]));                                     // 入力
                }
            }

            System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch();
            sw.Start();

            // 解析
            lstP.Sort();
            int iOut = 0;
            int iAdd = 0;
            if (lstP.Count == 0) { iOut = iX; }                                     // 数列空
            else
            {
                while (true)
                {
                    int iPus = iX + iAdd;                                           // Xに近い方からの整数プラス方面
                    int iMus = iX - iAdd;                                           // Xに近い方からの整数マイナ方面
                    Boolean bPus = true;
                    Boolean bMus = true;
                    for (int i = 0; i < lstP.Count; i++)                            // 数列内に存在すればなし
                    {
                        if (iPus == lstP[i]) { bPus = false; }
                        if (iMus == lstP[i]) { bMus = false; }
                    }
                    if      (bMus) { iOut = iMus; break; }                          // 数列内に存在しなければ終了マイナ方面が先
                    else if (bPus) { iOut = iPus; break; }                          // 数列内に存在しなければ終了プラス方面が後
                    iAdd += 1;                                                      // 次に近い整数
                }
            }

            // 出力
            System.Console.WriteLine("{0}", iOut.ToString().Trim());

            sw.Stop();
#if DEBUG
            Console.WriteLine();
            Console.WriteLine("{0}", sw.Elapsed.ToString());
            Console.WriteLine("続行するには何かキーを押してください．．．");
            Console.ReadKey();
#endif
    }

}