Draw a set of concentric circles

import turtle
radius = eval(input()) 
number = eval(input())   
cl = input()
turtle.pencolor(cl)
turtle.goto(0,0)
for i in range(number):
    turtle.circle(radius)
    radius=radius+20
    turtle.penup()
    turtle.goto(0, -20*(i+1))
    turtle.pendown()
turtle.hideturtle()
turtle.done()