gets.to_i.times{
    s = gets.chomp
    if s.count('G') != s.count('R')
        puts "impossible"
    else
        s.reverse =~ /R(.*?)G/
        if s.rindex('R') != s.length - 1 || $1.include?('W')
            puts "impossible"
        else
            loop{
                s.sub!(/G(.*?)R/){$1}
                if $&.nil?
                    break
                end
                }
                if s.include?('R')
                    puts "impossible"
                else
                    puts "possible"
                end
        end
    end
    }