while true
    h, w = gets.split( " " ).map { | val | val.to_i }
    break if 0 == h && 0 == w
     
    pa = [ "#", "." ]
    for i in ( 0 ... h ) 
        for j in ( 0 ... w )
            print( "#{pa[(i+j)&1]}" )
        end
        print( "\n" )
    end
    print( "\n" )
end