while true
    h, w = gets.split( " " ).map { | val | val.to_i }
    break if 0 == h && 0 == w
    pa1 = [ "#", "." ]
    pa2 = [ ".", "#" ]
    h.times { | i |
        if 0 == i%2
            w.times {  | i |
                print( "#{pa1[i&1]}" )
            }
            print( "\n" )
        else
            w.times {  | i |
                print( "#{pa2[i&1]}" )
            }
            print( "\n" )
        end
    }
    print( "\n" )
end