import math as m
x = float(input())
y = float(input())
z = float(input())
s = (x + y + z)/2
if max(x, y, z) == x and y + z > x:
    P = m.sqrt(s*(s - x)*(s - y) * (s - z))
    print(P)
elif max(x, y, z) == y and x + z > y:
    P = m.sqrt(s*(s - x)*(s - y) * (s - z))
    print(P)
elif max(x, y, z) == z and x + y > z:
    P = m.sqrt(s*(s - x)*(s - y) * (s - z))
    print(P)
else:
    print('Od ovih odsecaka se ne moze napraviti trougao')