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: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Xml;

namespace AtCoderPractice
{
    class ForbiddenList
    {
        static void Main(string[] args)
        {
            string[] input = Console.ReadLine().Split();
            int x = int.Parse(input[0]);
            int n = int.Parse(input[1]);
            if(n == 0)
            {
                Console.WriteLine(x);
                return;
            }
            int[] p = Console.ReadLine().Split().Select(int.Parse).ToArray();
            int min = 0;
            var lists = new List<int>();
            int[] diff;

            for(int i = 0; i <= 101; i++)
            {
                int frag = 0;
                for (int j = 0; j < n; j++)
                {
                    if(i == p[j])
                    {
                        frag = 1;
                        break;
                    }
                }
                if(frag != 1)
                {
                    lists.Add(i);
                }
            }
            diff = new int[lists.Count];
            for(int i = 0;i < lists.Count; i++)
            {
                diff[i] = Math.Abs(x - lists[i]);
                if(i == 0)
                {
                    min = lists[i];
                }
                else if (diff[i] < diff[i-1])
                {
                    min = lists[i];
                }
            }
            Console.WriteLine(min);
        }
    }
}