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: Wrong Answer)

using System;

namespace ABC170C
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] strs = Console.ReadLine().Split();
            int x = int.Parse(strs[0]);
            int n = int.Parse(strs[1]);
            string p = Console.ReadLine();
            if(p == "")
            {
                Console.WriteLine(x);
                Console.ReadLine();
                return;
            }
            int[] intP = Array.ConvertAll(p.Split(), int.Parse);
            Array.Sort(intP);
            int index = Array.BinarySearch(intP, x);
            if (index == -1)
            {
                Console.WriteLine(x);
                Console.ReadLine();
                return;
            }
            else
            {
                int i = 1;
                while (true)
                {
                    if (index - i < 0)
                    {
                        Console.WriteLine(x - i);
                        Console.ReadLine();
                        return;
                    }
                    else
                    {
                        if (intP[index-i] != x - i)
                        {
                            Console.WriteLine(x - i);
                            Console.ReadLine();
                            return;
                        }
                    }
                    if (index + i >= n)
                    {
                        Console.WriteLine(x + i);
                        Console.ReadLine();
                        return;
                    }
                    else
                    {
                        if (intP[index+i] != x + i)
                        {
                            Console.WriteLine(x + i);
                            Console.ReadLine();
                            return;
                        }
                    }
                    i++;
                }
            }
        }
    }
}