while hws = gets.chomp
    h,w = hws.split(' ').map{|n| n.to_i}
    if h==0 && w==0
        break
    else
        1.upto h do |i|
            if i.odd?
                if w.even?
                    puts "#."*(w/2)
                else
                    puts "#."*(w/2) + "#"
                end
            else
                if w.even?
                    puts ".#"*(w/2)
                else
                    puts ".#"*(w/2) + "."
                end
            end
        end
        puts ""
    end
end