#include <iostream>
#include <cstdio>
#include <string>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <memory.h>
#include <vector>
#include <algorithm>
#include <iomanip>


using namespace std;
vector<string> lt;
int main()  {
    freopen("triangles.in", "r", stdin);
    freopen("triangles.out", "w", stdout);
    long double a, b, c, S, sum = 0, p;
    cin >> a >> b >> c;
     p = (a + b + c) / 2;
     S = sqrt(p * (p - a)) * sqrt((p - b) *(p - c));
    sum += S;

    cin >> a >> b >> c;
     p = (a + b + c) / 2;
     S = sqrt(p * (p - a)) * sqrt((p - b) *(p - c));
        sum += S;
    cin >> a >> b >> c;
     p = (a + b + c) / 2;
   S = sqrt(p * (p - a)) * sqrt((p - b) *(p - c));
       sum += S;

    long double ans = sqrt(sum / 6);
       //cout << ans;return 0;
    printf("%.9f", double(ans));


    return 0;
}