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.Linq;
using System.Text;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Numerics;
using System.Runtime.CompilerServices;

namespace AtCoder
{
    class Program
    {

        const int BiggestMod = 1000000007;

        public static void Main()
        {

            var args = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();
            var memo = new bool[101];
            var x = args[0];

            if (args[1] != 0) args = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();
            else args = new int[0];

            for (int i = 0; i < 101; i++)
                memo[i] = false;

            foreach (var data in args)
                memo[data] = true;

            int min = int.MinValue, max = int.MaxValue;

            for (int i = x; 0 < i; i--)
                if (memo[i] == false)
                {
                    min = i;
                    break;
                }

            for (int i = x; i < 101; i++)
                if (memo[i] == false)
                {
                    max = i;
                    break;
                }

            if (max - x < x - min)
                Console.WriteLine(max);
            else
                Console.WriteLine(min);

        }

    }

}