while true

 h,w = gets.split(' ').collect{|n|n.to_i}
 break if h==0 && w==0
 h.times do |hc|
  char = hc % 2 == 1 ? '#' : '.' 
  w.times do
   print char
   char = char=='#'?'.':'#'   
  end
  puts
 end
 puts
end