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# (Mono-mcs 6.8.0.105) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        var inputs = Console.ReadLine().Split(' ');
        var X = int.Parse(inputs[0]);
        var N = int.Parse(inputs[1]);


        var nums = Console.ReadLine().Split(' ');
        var dict = new Dictionary<int, bool>();

        for(var i = 0; i <= 100; i++)
        {
            dict.Add(i, false); 
        }

        if (nums[0] != "")
        {
            foreach (var num in nums)
            {
                dict[int.Parse(num)] = true;
            }
        }

        var count = 0;
        var ans = X;
        while (true)
        {
            if(count == 0)
            {
                if (!dict[X])
                {
                    ans = X;
                    break;
                }
            }
            else
            {
                if(!dict.ContainsKey(X-count) || !dict[X - count])
                {
                    ans = X - count;
                    break;
                }
                if (!dict.ContainsKey(X + count) || !dict[X + count])
                {
                    ans = X + count;
                    break;
                }
            }

            count++;

        }


        Console.WriteLine(ans);
        Console.Read();
    }
}