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;

namespace C___Forbidden_List
{
    public class Program
    {
        static void Main(string[] args)
        {
            var a = Console.ReadLine();
            var b = Console.ReadLine();
            Console.WriteLine(DoMain(a, b));
        }

        public static int DoMain(string a, string b)
        {
            var c = a.Split(" ").Select(x => int.Parse(x)).ToList();
            var x = c[0];
            var n = c[1];
            if (n == 0)
            {
                return x;
            }

            var p = b.Split(" ").Select(x => int.Parse(x)).ToList();

            List<int> hundredList = new List<int>();
            for (int i = 0; i <= 101; i++)
            {
                hundredList.Add(i);
            }

            List<int> unhundredList = new List<int>();

            foreach (var item in hundredList)
            {
                if (!p.Contains(item))
                {
                    unhundredList.Add(item);
                }
            }

            List<int> diffList = new List<int>();
            foreach (var item in unhundredList)
            {
                diffList.Add(Math.Abs(x - item));
            }

            var min = diffList.Min();

            if (!p.Contains(x - min))
            {
                return x - min;
            }
            else
            {
                return x + min;
            }
        }
    }
}