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.Linq;

namespace AtCoder0614
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            string[] input = Console.ReadLine().Split(' ');
            string[] inputp = Console.ReadLine().Split(' ');

            int X = int.Parse(input[0]);
            int N = int.Parse(input[1]);

            int[] p = new int[N];
            int[] nonp = new int[200];
            int reigai = 0;
            for(var i =0; i<inputp.Length; i++)
            {
                if (inputp[i] != "")
                {
                    p[i] = int.Parse(inputp[i]);
                }
                else
                {
                    reigai = X;
                }
            }

            for (var i = -50; i < nonp.Length; i++) {
                for (var j = 0; j < nonp.Length; j++) {
                    if (!p.Contains(j)){
                        nonp[j] = j;
                    }
                }
             }
                //差の配列をxd を定義し、その最小値を求める
                int[] xd = new int[nonp.Length];

            for (var i = 0; i < nonp.Length; i++)
            {
                if (X >= nonp[i])
                {
                    xd[i] = X - nonp[i];
                }
                else
                {
                    xd[i] = nonp[i] - X;
                }
            }

            if (inputp[0] != "")
            {
                int min = xd[0];
                int minp = p[0];
                //xdが最小のものを調べる
                for (var i = 0; i < xd.Length; i++)
                {
                    if (min > xd[i])
                    {
                        min = xd[i];
                        minp = nonp[i];
                    }

                }
                {
                    Console.WriteLine(minp);
                }
            }
            else {
                Console.WriteLine(X);
            }

            }
    }
}