1 #include <cstdio>
 2 #include <cmath>
 3 #include <cstring>
 4 #include <cstdlib>
 5 #include <iostream>
 6 #include <sstream>
 7 #include <algorithm>
 8 #include <string>
 9 #include <queue>
10 #include <vector>
11 using namespace std;
12 const int maxn= 100;
13 const double eps= 1e-6;
14 const int inf = 0x3f3f3f3f;
15 const int mod =3;
16 typedef long long ll;
17 typedef long double ld;
18 int n,kase;
19 double ans;
20 int visit[maxn];
21 double a[maxn];
22 double judge(double x,double y,double z) //返回当前三条边 组成三角形的面积
23 {
24     if(x>y)                  
25         swap(x,y);
26     if(x>z)
27         swap(x,z);
28     if(y>z)
29         swap(y,z);
30     if(x+y<=z)                   //不能组成三角形 返回0
31         return 0.0;
32     else
33     {
34         double p=(x+y+z)/2;       //海伦公式
35         return sqrt(p*(p-x)*(p-y)*(p-z));
36     }
37 }
38 void dfs(int x,double y) //当前枚举x个三角形 总面积为y
39 {
40     ans=max(ans,y);
41     if(x==n/3)
42     {
43         x=0;
44         //printf("%d %lf\n",kase++,y);
45         y=0.0;
46     }
47     for(int i=1; i<=n; i++)
48     {
49         if(visit[i]==1)
50             continue;
51         for(int j=i+1; j<=n; j++)
52         {
53             if(visit[j]==1)
54                 continue;
55             for(int k=j+1; k<=n; k++)
56             {
57                 if(visit[k]==1)
58                     continue;
59                 else
60                 {
61                     visit[i]=1,visit[j]=1,visit[k]=1;
62                     dfs(x+1,y+judge(a[i],a[j],a[k]));
63                     visit[i]=0,visit[j]=0;visit[k]=0;
64                 }
65             }
66         }
67     }
68 }
69 int main()
70 {
71     while(scanf("%d",&n)!=EOF&&n)
72     {
73         for(int i=1;i<=n;i++)
74         {
75             scanf("%lf",&a[i]);
76         }
77         memset(visit,0,sizeof(visit));
78         ans=0.0;
79         //kase=1;
80         dfs(0,0.0);
81         printf("%.2lf\n",ans);
82     }
83 }