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;

class AtCoderCS {
    static void Main(string[] args) {
        int[] XN = Console.ReadLine().Split(' ').Select(i => int.Parse(i)).ToArray();
        int X = XN[0], N = XN[1];
        if (N == 0) {
            Console.WriteLine(X);
            return;
        }
        int[] p = Console.ReadLine().Split(' ').Select(i => int.Parse(i)).OrderBy(i => i).ToArray();

        bool[] table = Enumerable.Repeat(true, 102).ToArray();
        foreach (int i in p)
            table[i] = false;

        for (int i = 0; ; i++) {
            if (table[X - i]) {
                Console.WriteLine(X - i);
                return;
            } else if (table[X + i]) {
                Console.WriteLine(X + i);
                return;
            }
        }
    }
}