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.Generic;
using System.Linq;
public class Hello
{
    public static void Main()
    {
        //入力を保持する
        var XN = Console.ReadLine().Split().Select(e => int.Parse(e)).ToArray();
        var X = XN[0];
        var N = XN[1];
        //Ps配列が空の場合はXを出力して回答とする
        if (N == 0)
        {
            Console.WriteLine(X);
            return;
        }
        var Ps = Console.ReadLine().Split().Select(e => int.Parse(e)).ToArray();
        //Psを昇順に並び替える
        Array.Sort(Ps);
        //NのPs内に存在するかチェック
        var idx = Array.IndexOf(Ps, X);
        //NがPs配列に存在しない場合はXを出力して回答とする
        if (idx == -1)
        {
            Console.WriteLine(X);
            return;
        }

        //Ps内に含まれないXに最も近い数字を±1をしながら検索する
        var n = 1;
        while (true)
        {
            if (Array.IndexOf(Ps, X - n) == -1)
            {
                Console.WriteLine(X - n);
                break;
            }
            if (Array.IndexOf(Ps, X + n) == -1)
            {
                Console.WriteLine(X + n);
                break;
            }
            n += 1;

        }
    }
}