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.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;
using System.Text.RegularExpressions;
using System.Security.Policy;

namespace Yuzuki
{
    class Yukari
    {
        static int n, x;
        static string s, t;
        static int[] ps;

        public static void Main(string[] args)
        {
            input();

            HashSet<int> hs = new HashSet<int>(ps);
            
            for (int i = 0; i < 200; i++)
            {
                if (!hs.Contains(x - i))
                {
                    Console.WriteLine(x - i);
                    return;
                }
                if (!hs.Contains(x + i))
                {
                    Console.WriteLine(x + i);
                    return;
                }
            }

        }

        public static void input()
        {
            string[] buf = Console.ReadLine().Split();
            x = int.Parse(buf[0]);
            n = int.Parse(buf[1]);
            //s = buf[0];
            //t = buf[1];

            buf = Console.ReadLine().Split();
            ps = new int[n];
            for (int i = 0; i < n; i++)
            {
                ps[i] = int.Parse(buf[i]); 
            }
            Array.Sort(ps);
        }

    }
}