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)

#!/usr/bin/env perl

use strict;
use warnings;

my $XN = <STDIN>; chomp($XN);
my $PN = <STDIN>; chomp($PN);

my ( $X, $N ) = split qr(\s+), $XN;
my @nums = sort { $a <=> $b } split qr(\s+), $PN;

if ( $N == 0 ) {
  print $X, "\n";
  exit 0;
}

my %exists = map { $_ => 1 } @nums;

my $start = ( $X > $nums[$#nums] + 1 ) ? $X + 1 : $nums[$#nums] + 1 ;
my $diff = abs($X - ($nums[$#nums] + 1));
my $n = $nums[$#nums] + 1;

for ( my $x = $start + 1; $x > 1; $x-- ) {
  if ( exists $exists{$x} ) {
    next;
  }

  if ( abs($X - $x) <= $diff ) {
    $diff = abs($X - $x);
    $n = $x;
  }
}

print $n, "\n";