from math import pi

class Sirkel:
    def __init__(self, radius):
        self._radius = radius

    def diameter(self):
	# d = self._radius * 2
	# return d
	# OR:
        return self._radius * 2

    def omkrets(self):
	# o = self.diameter() * pi
	# return o
	# OR:
        return self.diameter() * pi

    def areal(self):
        #a = (self._radius**2) * pi
	#return a
	# OR:
        return (self._radius**2) * pi


def hovedprogram():
    s1 = Sirkel(5)
    print(s1.diameter())
    print(s1.omkrets())
    print(s1.areal())
hovedprogram()