10 CLS
20 SCREEN 8
30 FOR X = 1 TO 555
40 CIRCLE (X,X),X,X MOD 15
50 CIRCLE (300-X,X),X,X MOD 15
60 CIRCLE (300-X,200-X),X,X MOD 15
70 CIRCLE (X,200-X),X,X MOD 15
71 CIRCLE (X,X),X,0
72 CIRCLE (300-X,X),X,0
73 CIRCLE (300-X,200-X),X,0
74 CIRCLE (X,200-X),X,0
80 NEXT X