v = 0
w = 0
f = 0
x = -1
y = 1
s = 0
while true:
   v = Uniform(1-d, 1+d)
   w = Uniform(2-2*d, 2+2*d)
   f = Bernoulli(3/4)
   x = x + f*v
   y = y + f*w
   s = s + x*y
end