python畫漸變的圓

import turtle as t
n = eval(input())
t.penup()
t.goto(-350,0)
t.pendown()
t.pensize(2)
t.color("blue","yellow")
t.begin_fill()
for i in range(3,n):
    t.circle(50, steps=i)
    t.fd(100)
else:
    t.circle(50)
t.end_fill()
t.hideturtle()
t.done()