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;

namespace Atcoder2
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] tmp = Console.ReadLine().Split(' ');
            int X = int.Parse(tmp[0]);
            int all = int.Parse(tmp[1]);

            if (all == 0)
            {
                Console.WriteLine(X);
                return;
            }

            string[] tmpNums = Console.ReadLine().Split(' ');
            int[] nums = new int[all];
            for(int i = 0; i < all; i++)
            {
                nums[i] = int.Parse(tmpNums[i]);
            }

            int[] count = new int[100];
            foreach (int num in nums)
            {
                count[Math.Abs(X - num)] += 1;
            }

            for(int i = 0; i < 100; i++)
            {
                if (count[i] == 0)
                {
                    Console.WriteLine(X - i);
                    break;
                } else if (count[i] == 1)
                {
                    if (i != 0)
                    {
                        if (Array.IndexOf(nums, X - i) == -1)
                        {
                            Console.WriteLine(X - i);
                            break;
                        }
                        else
                        {
                            Console.WriteLine(X + i);
                            break;
                        }
                    }

                }
            }
        }
    }
}