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.Linq;
using System.Collections.Generic;

namespace Atcoder
{
    class Program
    {
        public static void Main(string[] args)
        {
            int[] input1 = Console.ReadLine().Split(" ").Select(i => int.Parse(i)).ToArray();
            int[] input2 = { 0 };
            if (input1[1] != 0)
            {
                input2 = Console.ReadLine().Split(" ").Select(i => int.Parse(i)).ToArray();
                var plusList = new List<long>();
                var minusList = new List<long>();
                foreach (var num in input2)
                {
                    var a = input1[0] - num;
                    if (a >= 0)
                        plusList.Add(a);
                    else
                    {
                        minusList.Add(a);
                    }
                };
                plusList.Sort();
                minusList.Sort();
                minusList.Reverse();
                int b = 0;
                foreach (var num in plusList)
                {
                    if (num != b)
                        break;
                    b++;
                }
                var ansa = input1[0] - b;
                int c = -1;
                foreach (var num in minusList)
                {
                    if (num != c)
                        break;
                    c--;
                }
                var ansb = input1[0] - c;

                if (Math.Abs(input1[0] - ansa) > Math.Abs(input1[0] - ansb))
                    Console.Write(ansb);
                else
                    Console.Write(ansa);
            }
            else
                Console.Write(input1[0]);
        }
    }
}