N = gets.to_i
W = gets.split.map(&:to_i).sort!

def f(n, ws)
  sum = 0; ws.each{ |w| sum += w }
  return false if sum.odd?

  dp = {}
  dp[0] = true

  ws.each do | w |
    dpc = dp.clone
    dpc.each do | k, v |
      dp[k+w] = dp[k]
    end
  end

  return dp[n/2]
end

puts f(N, W) ? 'possible' : 'impossible'