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;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.IO.Pipes;
using System.Linq;
using System.Numerics;

namespace Atcoder
{
	class Program
	{
		/*
			string s = Console.ReadLine();
			string[] ST = Console.ReadLine().Split(' ').ToArray();
			string S = strArray[0];
			string T = strArray[1];

			int[] HWN = Console.ReadLine().Split(' ').Select(i => int.Parse(i)).ToArray();
			int H = intArray[0];
			int W = intArray[1];
			int N = int.Parse(Console.ReadLine());

			List<int> A = new List<int>(Console.ReadLine().Split(' ').Select(i => int.Parse(i)).ToList());
			
			double[] R = Console.ReadLine().Split(' ').Select(i => double.Parse(i)).ToArray();

			Boolean ok = false;
			
			List<int> dp = Enumerable.Repeat(値, 個数).ToList();
			
			Console.WriteLine(ans);
			Console.WriteLine("Yes");
			Console.WriteLine("No");
			Console.ReadKey();
			Console.WriteLine(cnt);

			for(int i= 0; i < N; i++)
		*/

		static void Main(string[] args)
		{
			int[] XN = Console.ReadLine().Split(' ').Select(i => int.Parse(i)).ToArray();
			int X = XN[0];
			int N = XN[1];
			if(N == 0)
            {
				Console.WriteLine(X);
				return;
			}

			int[] P = Console.ReadLine().Split(' ').Select(i => int.Parse(i)).ToArray();

			int cnt = 0;
			while(true)
            {
				if(!P.Contains(X - cnt))
                {
					Console.WriteLine(X - cnt);
					return;
				}
                else if(!P.Contains(X + cnt))
                {
					Console.WriteLine(X + cnt);
					return;
				}
				cnt++;
            }
		}

		class Item : IComparable
		{
			public string A;
			public int B;
			public Item(string a, int b)
			{
				this.A = a;
				this.B = b;
			}
			public int CompareTo(object obj)
			{
				return B - ((Item)obj).B;
			}
		}

		/// <summary>
		/// 回文
		/// </summary>
		/// <param name="Target"></param>
		/// <param name="len"></param>
		/// <returns></returns>
		static bool Palindrome(string Target , int len)
        {
			bool yes = true;

			for(int i = 0;i < len; i++)
            {
				if(Target[i] != Target[len - 1 - i])
                {
					yes = false;
					break;
                }
            }
			return yes;
        }

		/// <summary>
		/// アナグラム
		/// </summary>
		/// <param name="word1"></param>
		/// <param name="word2"></param>
		/// <returns></returns>
		static bool IsAnagramOf(string word1, string word2)
		{
			char[] val1 = word1.ToCharArray();
			char[] val2 = word2.ToCharArray();
			Array.Sort(val1);
			Array.Sort(val2);
			word1 = new string(val1);
			word2 = new string(val2);

			return word1 == word2;
			//return word1.OrderBy(x => x).SequenceEqual(word2.OrderBy(x => x));
		}

		/// <summary>
		/// 最小公倍数
		/// </summary>
		/// <param name="a"></param>
		/// <param name="b"></param>
		/// <returns></returns>
		public static BigInteger Lcm(BigInteger a, BigInteger b)
		{
			return a * b / Gcd(a, b);
		}

		/// <summary>
		/// 最大公約数
		/// </summary>
		/// <param name="a"></param>
		/// <param name="b"></param>
		/// <returns></returns>
		public static BigInteger Gcd(BigInteger a, BigInteger b)
		{
			if (a < b)
				// 引数を入替えて自分を呼び出す
				return Gcd(b, a);
			while (b != 0)
			{
				var remainder = a % b;
				a = b;
				b = remainder;
			}
			return a;
		}
	}
}