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 Forbidden
{
    class Program
    {
        static void Main(string[] args)
        {
            int X, N;
            int[] p = new int[102];
            int[] r = new int[102];

            for (int i = 0; i <=  100; i++)
            {
                r[i] = 1;
            }

            string inD0 = Console.ReadLine();
            string[] cngD0 = inD0.Split(' ');

            X = int.Parse(cngD0[0]);
            N = int.Parse(cngD0[1]);

            string inD2 = Console.ReadLine();
            string[] cngD2 = inD2.Split(' ');

            for (int i = 0; i <= N - 1; i++)
            {
                p[i] = int.Parse(cngD2[i]);
                r[p[i] - 1] = 0;
            }

            int MaxD = p.Max();
            int MinD = p.Min();

            for (int i = 0; i <= MinD - 1; i++)
            {
                r[i] = 0;
            }

            for (int i = MaxD; i <= 100; i++)
            {
                r[i] = 0;
            }

            int j = X - 1;
            int gMin = 0;
            int gMax = 0;

            while (j > 0)
            {
                j--;
                if(r[j] == 1)
                {
                    gMin = j + 1;
                }
            }

            j = X - 1;
            while (j < 101)
            {
                j++;
                if (r[j] == 1)
                {
                    gMax = j;
                }
            }

            if (Math.Abs(X-gMin) <= Math.Abs(gMax - X))
            {
                Console.WriteLine(gMin);

            }
            else
            {
                Console.WriteLine(gMax);

            }
        }
    }
}