import sys
input = lambda : sys.stdin.readline().rstrip()
sys.setrecursionlimit(max(1000, 10**9))
write = lambda x: sys.stdout.write(x+"\n")

r,h,d = list(map(float, input().split()))
import math
a = math.asin(d/2/r)
ans = 2*h*r*r
s = d/2/r
c = (1-s**2)**0.5
ans0 = 2*h*r*r*(0.5*(math.pi/2-a) - (s*c)/2 - (c**3)/3)
v = 0
v += math.pi/4 - a/2
v += (0 - math.sin(2*a)/4)
v += (0 - math.cos(a)**3)/3
print(ans*v)