program weed
      implicit none
      real x,y,newx,newy,rand_num,ran2,sqr3_6
      integer maxit,ii,iseed,i_switch,pgopen,i_symbol
      external ran2

      if (pgopen('/xwin').le.0) stop
      call pgpap(6.0,1.0)
      call pgenv(-0.55,0.55,-0.05,1.05,1,-1)
      call pgsci(1)
      call pgscr(16,0.6,0.6,0.2)
      i_symbol = -1


 100  write(*,*) 'What is the total number of iteration ?'
      read (*,*) maxit
      write(*,*) 'Give a random seed integer :'
      read (*,*) iseed

      call pgsci(16)

      x = 0.0
      y = 1.0
      sqr3_6 = sqrt(3.0)/6

      DO 1000, II=1,MAXIT

c     call pgbbuf

c     do i=1,20
        rand_num = ran2(iseed)
        if (rand_num.gt.0.5) then
          newx = -0.5*x + sqr3_6*y
          newy = sqr3_6*x + 0.5*y
        else
          newx = -2*x/3 
          newy = (2*y + 1.0)/3
        endif
        x = newx
        y = newy
c     enddo
      call pgpt(1,x,y,i_symbol)

c      call pgebuf

 1000 CONTINUE


 104  write(*,*) 'More points to draw ? (1=YES;0=NO)'
      read (*,*) i_switch
      if (i_switch.eq.0) goto 102
      if (i_switch.eq.1) goto 100
      goto 104
 102  continue

      call pgclos

      end