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-csc 3.5.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using static System.Console;
using static System.Math;
using static System.Array;

class Program
{
    public static void Main()
    {
        var n = ReadLine().Split().Select(int.Parse).ToArray();
        if(n[1] < 1)
        {
            WriteLine(n[0]);
            return;
        }
        HashSet<int> list = new HashSet<int>();
        for(int i = -1; i <= 102; i++)
        {
            list.Add(i);
        }
        var m = ReadLine().Split().Select(int.Parse).ToArray();
        for(int i = 0; i < m.Length; i++)
        {
            list.Remove(m[i]);
        }
        if(list.Contains(n[0]))
        {
            WriteLine(n[0]);
            return;
        }
        for(int i = 1; i <= 102; i++)
        {
            if(n[0] - i >= -1)
            {
                if(list.Contains(n[0] - i))
                {
                    WriteLine(n[0] - i);
                    return;
                }
            }
            if(n[0] + i <= 102)
            {
                if(list.Contains(n[0] + i))
                {
                    WriteLine(n[0] + i);
                    return;
                }
            }
        }
    }
}