def zent(x,s)
    return if($f == 1)
    return if(s > $s)
    return if(x >= $n)
    if(s == $s)
        $f = 1; return;
    end
    zent(x+1,s)
    s += $a[x]
    zent(x+1,s)
end
$f = 0
$n=gets.chomp.to_i
$a=gets.chomp.split(" ").map(&:to_i).sort.reverse
$s = $a.inject(:+)
if ($s%2 == 1)
    puts "impossible"
    exit
end
$s = $s/2
zent(1,$a[0])
puts ($f == 1)? "possible" :"impossible"