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)

//Rextester.Program.Main is the entry point for your code. Don't change it.
//Microsoft (R) Visual C# Compiler version 2.9.0.63208 (958f2354)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            List<int> info = Cin();
            int x = info[0];
            int n = info[1];
            if (n == 0)
            {
                Cout(x);
                return;
            }
            
            List<int> nums = Cin().Distinct().OrderBy(t=>t).ToList();
            int idx = nums.IndexOf(x);
            if (idx == -1)
            {
                Cout(x);
                return;
            }
            
            int li = 0;
            int ri = nums.Count-1;
            // Left.
            for (int i = idx-1;i>=0; i--)
            {
                if (nums[i] + 1 != nums[i+1])
                {
                    li = i + 1;
                    break;
                }
            }
            // Right.
            for (int i = idx + 1; i < nums.Count; i++)
            {
                if (nums[i-1] + 1 != nums[i])
                {
                    ri = i - 1;
                    break;
                }
            }

            int left  = nums[li]-1;
            int right = nums[ri]+1;
            if(x - left <= right - x)
                Cout(left);
            else
               Cout(right); 
                     
        }
        
        public static List<int> Cin()
        {
            return Console.ReadLine().Split().Select(t => int.Parse(t)).ToList();
        }
        
        public static void Cout(int s)
        {
            Console.WriteLine(s);
        }
            
    }
}