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

cos = (pow(a,2)+pow(c,2)-pow(b,2))/(2*a*c)
sin = pow((1-pow(cos, 2)),1/2)

G = 8*b/sin
#2R*8, the laws of sine

print(a*c*sin/2-3*a*b*c/G)