a, b, c = map(int, input().split())

s = (a+b+c)/2
S = (s*(s-a)*(s-b)*(s-c))**0.5

cosa = (b**2+c**2-a**2)/(2*b*c)
cosb = (a**2+c**2-b**2)/(2*a*c)
cosc = (b**2+a**2-c**2)/(2*b*a)

sina = (1-cosa**2)**0.5
sinb = (1-cosb**2)**0.5
sinc = (1-cosc**2)**0.5

x = a/2
y = b/2
z = c/2
t1 = (y*z*sina)/2
t2 = (x*z*sinb)/2
t3 = (y*x*sinc)/2
print(S-(t1+t2+t3))