while line = gets
    h, w = line.chomp.split.map(&:to_i)
    #puts "#{h} #{w}"
    break if h == 0 && w == 0
    
    h.times do |i|
        w.times do |j|
            if (i == 0 && j == 0) || (i + j) % 2 == 0
                print "#"
            else
                print "."
            end
        end
        puts ""
    end
    puts ""
end