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;
using System.Text;
using System.Threading.Tasks;

namespace ACB170_C
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] xn = Console.ReadLine().Split(' ');
            int X = int.Parse(xn[0]);
            int N = int.Parse(xn[1]);
            List<int> p_list = new List<int>();
            int ans = X;

            if (0 < N)
            {
                p_list = Console.ReadLine().Split(' ').Select(v => int.Parse(v)).ToList();
                for (int i = 1; i < X; i++)
                {
                    if (!p_list.Contains(X - i))
                    {
                        ans = X - i;
                        break;
                    }
                    else if (!p_list.Contains(X + i))
                    {
                        ans = X + i;
                        break;
                    }
                }
            }

            Console.WriteLine(ans);
        }
    }
}