/* -*- coding: utf-8 -*-
 *
 * 1487.cc:  No.1487 ぺんぎんさんかっけー - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

/* typedef */

/* global variables */

/* subroutines */

/* main */

int main() {
  int a, b, c;
  scanf("%d%d%d", &a, &b, &c);

  double s = (a + b + c) * 0.5;
  double e = sqrt(s * (s - a) * (s - b) * (s - c)) / 4;
  printf("%.10lf\n", e);
  return 0;
}