w = 320
print "size: " + w + " x " + w
graphsize(w, w)
clg
color blue
for i=0 to w step 10
    color blue
    line w, i, (w - i), w
    color red
    line 0, (w-i), i, 0
    color green
    line i, 0, w, i
    color purple
    line 0, i, i, w
next i