HDU 5135(再思考)

#include<bits/stdc++.h>
using namespace std;

double store[15];
int n;

double cal(double a,double b,double c){
    double p = (a + b + c) / 2;
    return sqrt(p * (p - a) * (p - b) * (p - c));
}
bool judge(double a,double b,double c){
    return (fabs(a - b) < c && c < a + b);
}

int main(){
    while(scanf("%d",&n) == 1 && n){
        for(int i = 0;i < n;++i){
            scanf("%lf",&store[i]);
        }
        sort(store,store + n);
        double ans = 0;
        for(int i = n - 1;i >= 2;){
            double a = store[i],b = store[i - 1],
            c = store[i - 2];
            if(judge(a,b,c)){
                ans += cal(a,b,c);
                i -= 3;
            }
            else{
                --i;
            }
        }
        printf("%.2lf\n",ans);
    }
    return 0;
}