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;

public class Hello
{
    public static void Main()
    {
        hoge();
        System.Console.ReadLine();
    }

    public static void hoge()
    {
        var vars = System.Console.ReadLine().Split(' ').Select(long.Parse).ToArray();

        var x = vars[0];
        var n = vars[1];
        if (n == 0)
        {
            System.Console.ReadLine();
            Console.WriteLine(x);
            return;
        }
        var p = System.Console.ReadLine().Split(' ').Select(long.Parse).ToArray();
        
        var ans = Enumerable.Range(1, 100).Where(v => !p.Contains(v)).ToList();
        ans.Add(0);
        ans.Add(-1);
        ans = ans.OrderByDescending(v => v).ToList();

        var sa = int.MaxValue;
        var kotae = -1;
        foreach(var v in ans)
        {
            if(Math.Abs(v - x) <= sa)
            {
                kotae = v;
                sa = (int)Math.Abs(v - x);
            }
        }

        Console.WriteLine(kotae);

    }
}