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 AtCoder.Abcdef
{
    public class QuestionC
    {
        public static void Main(string[] args)
        {
            var sw = new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(sw);

            //Input int array
            int[] inputArray = Console.ReadLine().Split(' ').Select(i => int.Parse(i)).ToArray();
            int x = inputArray[0];
            int n = inputArray[1];
            
            if (n == 0) 
            {
                Console.WriteLine(x.ToString());
                return;
            }

            var hashSet = Console.ReadLine().Split(' ').Select(i => int.Parse(i)).ToHashSet<int>();

            //Write Code
            bool foundUpper = false, foundLower = false;
            int lowerResult = 0, upperResult = 0;
            int diff = 0;
            while (foundUpper == false && foundUpper == false) 
            {
                if (!hashSet.Contains(x - diff))
                {
                    foundLower = true;
                    lowerResult = x - diff;
                }
                if (!hashSet.Contains(x + diff)) 
                {
                    foundUpper = true;
                    upperResult = x + diff;
                }
                diff++;
            }

            if (foundLower == true)
            {
                Console.WriteLine(lowerResult.ToString());
            }
            else
            {
                Console.WriteLine(upperResult.ToString());
            }

            Console.Out.Flush();
        }
    }
}