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)

namespace atcoder
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Runtime.CompilerServices;
    using static System.Math;
    using static Ex;
    class Program
    {
        static void Main(string[] args) => new Program().Solve();

        void Solve()
        {
            var t1 = GetInputs.AsInt().ToArray();
            var X = t1[0];
            var N = t1[1];
            if (N == 0) {
                Console.WriteLine(X);
            }
            else
            {
                var p = new HashSet<int>(GetInputs.AsInt());

                Console.WriteLine(
                    Enumerable.Range(-1, 200)
                        .Select(x => (x, Abs(X - x)))
                        .OrderBy(x => x.Item2)
                        .Where(x => !p.Contains(x.x))
                        .First().x
                );
            }
        }

    }

    static class Ex
    {
        public static IEnumerable<string> GetInputs => Console.ReadLine().Split();
        public static IEnumerable<int> AsInt(this IEnumerable<string> xs) => xs.Select(int.Parse);
    }

}