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.Linq;
using static System.Console;

namespace C
{
    internal class Program
    {
        public static void Main(string[] args)
        {
            var xn = ReadLine().Split(' ').Select(int.Parse);
            if (xn.Last() == 0)
            {
                WriteLine(xn.First());
                return;
            }

            var pList = ReadLine().Split(' ').Select(int.Parse).ToList();
            var target = xn.First();
            if (!pList.Contains(target))
            {
                WriteLine(target);
                return;
            }

            int CheckDecrement(int t)
            {
                t--;
                if (!pList.Contains(t)) return t;
                pList.Remove(t);
                return CheckDecrement(t);
            }
            int CheckIncrement(int t)
            {
                t++;
                if (!pList.Contains(t)) return t;
                pList.Remove(t);
                return CheckIncrement(t);
            }

            var lower =CheckDecrement(target);
            var higher =CheckIncrement(target);
            var lDist = Math.Abs(lower - target);
            var hDist = Math.Abs(higher - target);
            if (lDist == hDist)
            {
                WriteLine(lower);
            }
            else
            {
                WriteLine(lDist < hDist ? lower : higher);
            }
        }
    }
}