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;
using System.Collections.Generic;
using System.IO;
using System.Linq;

namespace AtCoder
{
	public class ABC
	{
		static public void Main(string[] args)
		{
			Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
			Solve(args);
			Console.Out.Flush();
		}

		const int mod = 1000000007;  // 10^9+7
		static int Mod(long x, int m) { return (int)((x % m + m) % m); }
		static long Mod(long x, long m) { return (x % m + m) % m; }

		static public void Solve(string[] args)
		{
			//string s = Console.ReadLine();
			//int n = int.Parse(Console.ReadLine());
			//long x = long.Parse(Console.ReadLine());
			//int[] vs = Console.ReadLine().Split().Select(int.Parse).ToArray();
			//long[] vs = Console.ReadLine().Split().Select(long.Parse).ToArray();

			int[] vs = Console.ReadLine().Split().Select(int.Parse).ToArray();
			int x = vs[0];
			int n = vs[1];
			if (n == 0) {
				Console.WriteLine(x);
				return;
			}
			HashSet<int> hs = Console.ReadLine().Split().Select(int.Parse).ToHashSet();

			int ans = x;
			int i = 0;
			while (true) {
				if (!hs.Contains(x - i)) {
					ans = x - i;
					break;
				} else if (!hs.Contains(x + i)) {
					ans = x + i;
					break;
				}
				i++;
			}
			Console.WriteLine(ans);
		}
	}
}