# -*- coding:utf-8 -*-
# @Author len
# @Create 2023/12/14 20:16

a, b, c = map(float, input("请输入三角形的三边长（用空格分隔）: ").split())

p = (a + b + c) / 2
area = (p * (p - a) * (p - b) * (p - c)) ** 0.5
print(area)