use strict;
use warnings;

my $num = <STDIN>;
my @w = split(' ', <STDIN>);


my $sum = eval join('+', @w);

my %p = (0 => 0);
my %n = %p;

my $ans = 'impossible';

if($sum%2 == 0){
  my $half = $sum/2;
  my %pair = (slct => 0, rest => 0);

  LOOP: for my $i (@w){
    for my $j (keys %p){
      $pair{slct} = $j + $i;
      next if($pair{slct} > $half);
      if(!defined($n{$pair{slct}})){
        $pair{rest} = $sum - $pair{slct};
        if($pair{slct} == $pair{rest}){
          $ans = 'possible';
          last LOOP;
        }else{
          $n{$pair{slct}} = $pair{rest};
        }
      }
    }
    %p = %n;
  }
}

print $ans;