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.IO;
using System.Linq;
using System.Collections.Generic;
using System.Text;
using System.Numerics;

namespace abc170
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
            if (File.Exists("input.txt"))
            {
                Console.SetIn(new StreamReader("input.txt"));
            }
            solve_abc170C();
            Console.Out.Flush();
        }

        public static void solve_abc170C()
        {
            int[] xn = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
            int x = xn[0];
            int n = xn[1];
            if (n == 0)
            {
                Console.WriteLine(x);
            }
            else
            {
                int[] p = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
                Dictionary<int, int> dic = new Dictionary<int, int>();
                for (int i = 0; i < n; i++)
                {
                    dic.Add(p[i], p[i]);
                }
                int minLeft = x - 1;
                int minRight = x + 1;
                while (dic.ContainsKey(minLeft))
                {
                    minLeft--;
                }
                while (dic.ContainsKey(minRight))
                {
                    minRight++;
                }
                int dLeft = Math.Abs(x - minLeft);
                int dRight = Math.Abs(x - minRight);
                int min = Math.Min(minLeft, minRight);
                if (dLeft > dRight)
                {
                    min = minRight;
                }
                else if (dLeft < dRight)
                {
                    min = minLeft;
                }
                Console.WriteLine(min);
            }
        }

        public static void solve_abc170B()
        {
            int[] xy = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
            int x = xy[0];
            int y = xy[1];
            double a = (double)(y - (2 * x)) / 2;
            double b = x - a; 
            if (y % 2 != 0)
            {
                Console.WriteLine("No");
            }
            else if (a >= 0 && b >= 0 && a + b == x)
            {
                Console.WriteLine("Yes");
            }
            else
            {
                Console.WriteLine("No");
            }
        }

        public static void solve_abc170A()
        {
            int[] x = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
            for (int i = 0; i < x.Length; i++)
            {
                if (x[i] == 0)
                {
                    Console.WriteLine(i + 1);
                    break;
                }
            }
        }
    }
}