Pi = 3.1415926535897932384626433832795
from math import *
side, R = [int(x) for x in str(input()).split(' ')]
if (R <= side/2):
    print(Pi*R*R)
elif (2**0.5*side/2<=R):
    print(side*side)
else:
    d = side/2
    S = R*R*acos(d/R) - d*sqrt(R*R-d*d)
    print(Pi*R*R-4*S)