HDU 1411 校庆神秘建筑 (求四面体体积)

/************************************
 * Author : binwin20                *
 * Blog   : blog.csdn.net/binwin20  *
 ************************************/
#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <cstdio>
#include <cmath>
#include <cstring>
#include <iostream>
#include <queue>
#include <map>
#include <stack>
#include <string>
#include <algorithm>
#include <vector>
#include <list>
#include <deque>

#define LL long long
#define DB double
#define SI(a) scanf("%d",&a)
#define SD(a) scanf("%lf",&a)
#define SS(a) scanf("%s",a)
#define PF printf
#define MM(a,b) memset(a,b,sizeof(a))
#define REP(i,a,b) for(int i=a;i<b;i++) 
#define REPD(i,a,b) for(int i=a;i>b;i--)
#define INF 0x3f3f3f3f
#define EPS 1e-8
#define bug puts("bug")
using namespace std;
#define N 100
DB q,p,r,l,m,n;
int main()
{
    #ifndef ONLINE_JUDGE
    freopen("in.txt","r",stdin);
    #endif
    while(~SD(p){
        SD(q),SD(r),SD(n),SD(m),SD(l);
        p = p*p;
        q = q*q;
        r = r*r;
        l = l*l;
        m = m*m;
        n = n*n;
        DB ans = sqrt((4*p*q*r-p*(q+r-l)*(q+r-l)-q*(r+p-m)
            *(r+p-m)-r*(p+q-n)*(p+q-n)+(p+q-n)*(q+r-l)*(r+p-m)))/12.0;
        PF("%.4lf\n",ans);
    } return 0;
}