Name ... is not defined. How do i define it?

Name ... is not defined. How do i define it?

p=3.14159
#Fuction to circleArea
def circleArea(A):
A=r*r*p
radius=r
return radius
#Main Program
r=int(input("Enter radius: "))
print("The area of the circle is:" )
print(circleArea(A))
Problem: print(circleArea(A)) NameError: name 'A' is not defined