3
1 1 20
7
3 4 5 3 4 5 90
0

0.00
13.64

#include <cstdio>
#include <cmath>
#include <algorithm>
using namespace std;
int const MAX = (1 << 13);
int ok[MAX], a[105];
double re[MAX], dp[MAX];

bool judge(int a, int b, int c)
{
    if(a + b > c && a + c > b && b + c > a)
        return true;
    return false;
}

double area(int a, int b, int c)
{
    double p = (a + b + c) / 2.0;
    return sqrt(p * (p - a) * (p - b) * (p - c));
}

int main()
{
    int n;
    while(scanf("%d", &n) != EOF && n)
    {
        int cnt = 0;
        bool flag = false;
        memset(dp, 0, sizeof(dp));
        memset(re, 0, sizeof(re));
        for(int i = 0; i < n; i++)
            scanf("%d", &a[i]);
        sort(a, a + n);
        for(int i = 0; i < n; i++)
            for(int j = i + 1; j < n; j++)
                for(int k = j + 1; k < n; k++)
                    if(judge(a[i], a[j], a[k]))
                    {
                        flag = true;
                        ok[cnt] = ((1 << i) | (1 << j) | (1 << k));
                        re[cnt++] = area(a[i], a[j], a[k]);
                    }
        if(!flag)
        {
            printf("0.00\n");
            continue;
        }
        for(int i = 0; i <= MAX; i++)
            for(int j = 0; j < cnt; j++)
                if(!(i & ok[j]))
                    dp[(i | ok[j])] =  dp[i] + re[j];
        double ans = 0.0;
        for(int i = 0; i <= MAX; i++)
            ans = max(ans, dp[i]);
        printf("%.2f\n", ans);
    }
}