while true
    h, w = gets.chomp.split.map(&:to_i)
    break if h == 0 && w == 0

    h.times{|y|
        w.times{|x|
            if y.even?
                print "#" if x.even?
                print "." if x.odd?
            else
                print "." if x.even?
                print "#" if x.odd?
            end
        }
        puts
    }
    puts
end