import math
def circle(question):
    error = "error!"

    while True:
        try:
            response=float(input(question))
            if response > 0:
                    return response
            else:
                print(error)
        except ValueError:
            print(error)

radius = circle("Enter radius: ")

circumfrence = 2*math.pi*radius
area =math.pi*radius*radius
print(f"Circumference: {circumfrence:.2f} ")
print(f"Area: {area:.2f} ")