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;

using E = System.Linq.Enumerable;

public class Program
{
    public static void Main()
    {
        var xn = Console.ReadLine().Split().Select(x => int.Parse(x)).ToArray();
        var (varX, varN) = (xn[0], xn[1]);
        var seqP = varN == 0 ? Array.Empty<int>() : Console.ReadLine().Split().Select(x => int.Parse(x)).ToArray();

        var set = new HashSet<int>(seqP);
        int lesser = varX;
        int greater = varX;
        var z = int.MaxValue;
        while (z == int.MaxValue)
        {
            if (!set.Contains(lesser))
            {
                z = lesser;
                break;
            }

            if (!set.Contains(greater))
            {
                z = greater;
                break;
            }

            --lesser;
            ++greater;
        }

        Console.WriteLine(z);
    }
}