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;
using static Scanner;

class Program
{
    static void Main() => new Program().Solve();

    public void Solve()
    {
        var x = ReadInt();
        var n = ReadInt();
        if (n == 0)
        {
            Console.WriteLine(x);
            return;
        }
        var p = Enumerable.Range(0, 102).Except(ReadInt(n)).OrderBy(y => y).ToArray();
        var a = Array.BinarySearch(p, x);
        if (a >= 0)
        {
            Console.WriteLine(x);
            return;
        }
        var b = ~a - 1;
        var c = b + 1;
        if (x - p[b] <= p[c] - x)
        {
            Console.WriteLine(p[b]);
        }
        else
        {
            Console.WriteLine(p[c]);
        }
    }
}

static class Scanner
{
    static Queue<string> que = new Queue<string>();

    public static string Read()
    {
        if (!que.Any())
        {
            foreach (var s in Console.ReadLine().Split()) que.Enqueue(s);
        }
        return que.Dequeue();
    }
    public static int ReadInt() => int.Parse(Read());
    public static long ReadLong() => long.Parse(Read());
    public static double ReadDouble() => double.Parse(Read());
    public static decimal ReadDecimal() => decimal.Parse(Read());

    public static IEnumerable<string> Read(long n)
    {
        for (long i = 0; i < n; i++) yield return Read();
    }
    public static IEnumerable<int> ReadInt(long n) => Read(n).Select(int.Parse);
    public static IEnumerable<long> ReadLong(long n) => Read(n).Select(long.Parse);
    public static IEnumerable<double> ReadDouble(long n) => Read(n).Select(double.Parse);
    public static IEnumerable<decimal> ReadDecimal(long n) => Read(n).Select(decimal.Parse);
}