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 static System.Math;
using System;

public class Hello
{
    public static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var x = int.Parse(line[0]);
        var n = int.Parse(line[1]);
        if (n == 0) { Console.WriteLine(x); goto exit; }
        line = Console.ReadLine().Trim().Split(' ');
        var p = Array.ConvertAll(line, int.Parse);
        getAns(x, n, p);
    exit:;
    }
    static void getAns(int x, int n, int[] p)
    {
        var c = new bool[102];
        for (int i = 0; i < n; i++) c[p[i]] = true;
        var r = 0; var L = 0;
        for (int i = x; i <= 101; i++)
            if (!c[i]) { r = i; break; }
        for (int i = x; i >= 0; i--)
            if (!c[i]) { L = i; break; }
        Console.WriteLine(Abs(x - L) <= Abs(x - r) ? L : r);
    }
}