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.*;
class Main
{
  public static void main(String [] args)
  {
    Scanner s = new Scanner(System.in);
   int num = s.nextInt();
    int n = s.nextInt();
    
    HashSet<Integer>h = new HashSet<>();
    
   	for(int i = 0; i < n;i++)
      h.add(s.nextInt());
    
    int count = 1;
    boolean found = false;
    int prev = 1;
    
    while(!found)
    {
      if(!(h.contains(num - count))) found = true;
      prev = count; 
      if(count > 0)
           count = 0 - count;
      else
           count = 0 - count + 1;
    }
           
    System.out.println(num - prev);
                          
  }
}