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.*;
import java.math.BigDecimal;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int x = sc.nextInt();
        int n = sc.nextInt();
        int check = n;
        int z= 999;
        int p[] = new int[n];
        int ans = 100;
        HashSet hs = new HashSet();
        for(int i = 0; i < n;i++){
          hs.add(sc.nextInt());
        }
        
        hs.add(x);
        if(hs.size() != n){
          System.out.println(x);
          System.exit(0);
        }
        for(int i = -100; i <= 100;i++){
          hs.add(i);
          if(hs.size() != check){
            if(Math.abs(x - i) < ans){
              ans = x - i;
              z = i;
            }
            check++;
          }
        }
        

        System.out.println(z);
    }
}