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 Java (OpenJDK 11.0.6) (judge verdict: Wrong Answer)

import java.util.Scanner;
import java.util.SortedSet;
import java.util.TreeSet;

public class Main {

	static Main instance = new Main();

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		//入力値取得
		int X = scan.nextInt();
		int N = scan.nextInt();

		int[] pList = new int[N];

		for (int i = 0; i < N; i++) {
			pList[i] = scan.nextInt() - X;
		}

		//WK変数
		SortedSet<Integer> set = new TreeSet<>();

		for (int i = -500; i <= 500; i++) {
			set.add(i);
		}

		for (int i = 0; i < N; i++) {
			set.remove(pList[i]);
		}

		//演算
		int result = 0;

		if (set.contains(0)) {
			result = X;
		}

		int idx = 1;

		while (result == 0) {
			if (set.contains(idx)) {
				result = X + idx;
			}

			if (set.contains(-idx)) {
				result = X - idx;
			}

			idx++;
		}

		//結果出力
		System.out.println(result);
	}
}