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 System.Console;
using static System.Math;

namespace C_ABC170
{
    class MainClass
    {

        static int[] s, p;

        public static void Main(string[] args)
        {
            s = Array.ConvertAll(ReadLine().Split().ToArray(), int.Parse);
            if (s[1] > 0)
            {
                p = Array.ConvertAll(ReadLine().Split().ToArray(), int.Parse);
            }
            int x = s[0];
            int n = s[1];
            int[] xplus = new int[200];
            int[] xminus = new int[200];
            int xzero = 0;
            for (int i = 0; i < n; i++)
            {
                int div = x - p[i];
                if (div == 0)
                {
                    xzero = -1;
                }
                else if (div > 0)
                {
                    xplus[div] = -1;
                }
                else
                {
                    xminus[-div] = -1;
                }
            }
            if (xzero == 0)
            {
                WriteLine(x);
                return;
            }
            for (int i = 1; i < 200; i++)
            {
                if (xplus[i] == 0)
                {
                    WriteLine(x - i);
                    return;
                }
                else if (xminus[i] == 0)
                {
                    WriteLine(x + i);
                    return;
                }
            }

        }
    }
}