渐变的圆

import turtle
a=int(input())
turtle.setup(600,400,500,200)
turtle.pensize(2)
turtle.color("blue")
turtle.fillcolor("yellow")
i=3
while i<=a:
    turtle.penup()
    turtle.goto(-600+100*i,-10)
    turtle.begin_fill()
    turtle.pendown()
    turtle.circle(50,steps=i)
    turtle.end_fill()
    turtle.fd(100)
    i=i+1
turtle.penup()
turtle.goto(-600+100*i,-10)
turtle.begin_fill()
turtle.pendown()
turtle.circle(50)
turtle.end_fill()
turtle.hideturtle()
turtle.done()