gets.to_i.times{
    s = gets.chomp
    s.reverse =~ /R(.*?)G/
    tmp = s.count('G')
    if s[-1] != 'R' || s[0] != 'W' || $1.to_s.include?('W') || tmp != s.count('R') || s.count('W') < tmp
        puts "impossible"
    else
        flag = 0
        s.delete!('W')
        g = []
        r = []
        (tmp * 2).times{|i|
            case s[i]
                when 'G'
                g.push(i)
                when 'R'
                r.push(i)
            end
            }
        tmp.times{|i|
            if g[i] > r[i]
                flag = 1
            end
            }
        puts ["possible","impossible"][flag]
    end
    }