# W->G->R
T = gets.to_i
S = T.times.map{ gets.rstrip.chars }

S.each do | s |
  #
  if s.count('G') != s.count('R') || s.count('G') > s.count('W')
    puts 'impossible'
    next
  end

  #
  to_skip = false
  que = []
  s.each do | c |
    case c
    when 'W'
      # nop
    when 'G'
      if que.count('W') <= que.count('G')
        puts 'impossible'
        to_skip = true
        break
      end
    when 'R'
      if que.count('G') <= que.count('R')
        puts 'impossible'
        to_skip = true
        break
      end
    end
    que << c
  end

  puts 'possible' unless to_skip
end