INPUT r
INPUT a, b
SCREEN 7, , 0, 1
 
x = a
y = a
sx = 8
sy = 5
 
WHILE INKEY$ = ""
        PCOPY 0, 1
        CIRCLE (x, y), r, 0
        PAINT (x, y), 0
 
        x = x + sx
        y = y + sy
 
        CIRCLE (x, y), r, 15
        PAINT (x, y), 15
 
        IF y > b OR y < a THEN sy = -sy: sx = -sx
 
        t = TIMER
        WHILE t = TIMER
        WEND
WEND