SUB MAIN
  DIM CX, CY, R AS INTEGER
  
  GRAPHICS
  
  CY=SCREENHEIGHT()/2
  CX=SCREENWIDTH()/2
  
  IF (CX < CY) THEN
    R=CX/2
  ELSE
    R=CY/2
  END IF
  
  SETCOLOR 0,0,0
  CLS
  SETCOLOR 255,255,255
  DRAWCIRCLE CX,CY,R
  REPAINT
  SLEEP 5000
END SUB