DEFDBL A-Z
SCREEN 13
pi = 3.141285

p1 = -1
p2 = 4
mi = 0
dia = 1.5
tli = 0
bli = -1

siz = 100 / dia
FOR a = 0 TO 100 STEP 100 / dia
  LINE (0, 100 + a)-(319, 100 + a), 2
  LINE (0, 100 - a)-(319, 100 - a), 2
NEXT a

LINE (0, 100)-(319, 100), 10
ste = (p2 - p1) / 319
o = 0
FOR x = p1 TO p2 STEP ste / 20

  y = x ^ 2 - 3 * x

u = ABS(INT(x) - x)
IF u >= lu THEN su = 1 ELSE su = 0
lu = u
rx = (x - p1) * (1 / ste)
IF lsu > su THEN tl = 1
lsu = su
y = y - mi
IF y > tli THEN y = tli
IF y < bli THEN y = bli
s = s + ABS(y)
ry = -y * siz + 100
IF ry > 199 THEN ry = 199
IF ry < 0 THEN ry = 0
o = o + 1
IF o = 20 THEN
  o = 0
  IF tl = 1 THEN LINE (rx, 0)-(rx, 199), 4: tl = 0
  LINE (rx, 100)-(rx, ry), 15
END IF
NEXT x
LOCATE 1, 1
PRINT s / (1 / ste) / 20