# Here your code !
n=gets.chomp.to_i
a=gets.chomp.split(" ").map(&:to_i)
s = 0
t = 0
a.sort!.reverse!
a.each do |d|
    if(s > t)
        t += d
    else
        s += d
    end
end
if(s == t)
    puts "possible"
elsif(((s - t) % 2) == 1)
    puts "impossible"
else
    puts (a.include?((s-t).abs/2))? "possible" : "impossible"
end