import math
p = math.pi

def surface(x):
    d = 10**-5
    x2 = int(x * 100000)
    b = 10**5 - x2
    ans = 0
    for i in range(b):
        ans += 2 * p * d * ( 1 - ( (1-d*i)**2 ) ** 0.5 )
    return ans

a, b = float(input()), float(input())
if a >= 0:
    print( surface(a) - surface(b) )
elif b >= 0:
    print( 4*p - surface(b) - surface(-a) )
else:
    print( surface(-b) - surface(-a) )