from math import pi
from turtle import Turtle, exitonclick, speed
fred = Turtle()
speed(10)


def polygon(n, side):
    angle = 360.0 / n
    for i in range(n):
        fred.forward(side)
        fred.left(angle)


# kruznici aproximuje pomoci 360-uhelnika
# porovnanim obvodu: 360*side = 2*pi*r
def circle(r):
    side = 2 * pi * r / 360
    polygon(360, side)

circle(90)
exitonclick()