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 Perl (5.26.1) (judge verdict: Wrong Answer)

use strict;
use warnings;
use feature 'say';
use Data::Dumper;

chomp(my $line  = <STDIN>);
my ($x, $n) = split / /, $line;

if($n == 0) {
  say $x;
  exit;
}

chomp(my $line2 = <STDIN>);
my @nums = sort { $a <=> $b } (split/ /, $line2);

my %exist_hash = ();
map { $exist_hash{$_}++ } @nums;

my @all = ();
my $i = $nums[0];
while($i <= $nums[-1]) {
  push(@all, $i);
  $i++;
}

my @not_exist = ();
for (@all) {
  if(! exists($exist_hash{$_}) ) {
    push(@not_exist, $_);
  }
}

my $min_diff = 100;
my $answer = 0;

for my $num ( sort { $b <=> $a } @not_exist) {
  my $diff = abs($x) - abs($num);
  if ( abs($diff) <= $min_diff) {
    if ($answer = 0 || $num < $answer ) {
      $answer = $num;
    }
    $min_diff = abs($diff);
  }
}

say $answer;