r = float(input("Radius = "))
pi = 3.14159265359
s = pi*r*r
print("Area = ", s)

    ============== RESTART: C:\area of a circle fa.py =============
    Radius = 1
    Area =  3.14159265359
>>>
    ============== RESTART: C:\area of a circle fa.py =============
    Radius = 2.5
    Area =  19.634954084937497
>>>
    ============== RESTART: C:\area of a circle fa.py =============
    Radius = 643
    Area =  1298888.341034132
>>>
    ============== RESTART: C:\area of a circle fa.py =============
    Radius = 0
    Area =  0.0
>>>