def cbit(x);x.to_s(2).chars.count("1");end

n=gets.to_i

w=gets.split(" ").map(&:to_i).sort!
s=w.inject(:+)

if s%2==1;puts "impossible";exit;end
if s/2<w[-1];puts "impossible";exit;end

(1..n).each{|i|w.combination(i).each{|c|if c.inject(:+)==s/2;puts "possible";exit;end}}

puts "impossible"