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;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.Design;
using System.IO.Compression;
using System.Linq;
using System.Numerics;
using System.Text;
using Console = System.Console;

namespace Atcoder
{
    class Program
    {
        private const long COMDIV = 1000000007;

        static void Main(string[] args)
        {
            var XN = Console.ReadLine().Split().Select(int.Parse).ToArray();
            if (XN[1] == 0)
            {
                Console.WriteLine(XN[0]);
                return;
            }
            var Ps = Console.ReadLine().Split().Select(int.Parse).OrderBy(x => x).ToArray();
            int ret = int.MaxValue;
            int preDis = int.MaxValue;
            for (int i = 0; i <= 100; i++)
            {
                var dis = Math.Abs(XN[0] - i);
                if (!Ps.Contains(i) && preDis > dis)
                {
                    preDis = dis;
                    ret = i;
                }
            }

            if (ret == int.MinValue)
            {
                Console.WriteLine(0);
                return;
            }
            Console.WriteLine(ret);
        }
    }
}