3D Convex Hall

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>

#include<sstream>
#include<iostream>
#include<string>
#include<algorithm>
#include<vector>
#include<utility>
#include<queue>
#include<stack>
using namespace std;

#define ABS(a) (((a)>0)?(a):-(a))
#define MAX(a,b) (((a)>(b))?(a):(b))
#define MIN(a,b) (((a)<(b))?(a):(b))

typedef __int64 LL;

typedef pair<int,int> PII;
typedef pair<int,PII> PIP;
typedef pair<PII,int> PPI;
typedef pair<PII,PII> PPP;

typedef string str;

struct Point
{
LL x,y,z;
};

Point p[30];

#define S(X) ((X)*(X))
#define D(a,b) ( sqrt( S(p[a].x-p[b].x) + S(p[a].z-p[b].z) + S(p[a].y-p[b].y) ) )

double area(int a,int b,int c)
{
double s1 = D(a,b);
double s2 = D(c,b);
double s3 = D(a,c);
double s = (s1+s2+s3)/2.;

return sqrt(s*(s-s1)*(s-s2)*(s-s3));
}

LL FIND(int a,int b,int c,int d)
{
LL x1 = p[a].x, y1=p[a].y, z1=p[a].z;
LL x2 = p[b].x, y2=p[b].y, z2=p[b].z;
LL x3 = p[c].x, y3=p[c].y, z3=p[c].z;
LL x4 = p[d].x, y4=p[d].y, z4=p[d].z;

return (x4-x1)*(y2-y1)*(z3-z1)
+ (y4-y1)*(z2-z1)*(x3-x1)
+ (z4-z1)*(x2-x1)*(y3-y1)
- (x4-x1)*(z2-z1)*(y3-y1)
- (y4-y1)*(x2-x1)*(z3-z1)
- (z4-z1)*(y2-y1)*(x3-x1);
}

int main()
{
double ans;
LL temp;
int pos,neg,i,j,k,m,n,T,ks=0;


while(scanf("%d",&n)!=EOF && n)
{
ks++;
for(i=0;i<n;i++)
scanf("%I64d%I64d%I64d",&p[i].x,&p[i].y,&p[i].z);

ans = 0;
for(i=0;i<n;i++)
for(j=i+1;j<n;j++)
for(k=j+1;k<n;k++)
{
pos=neg=0;
for(m=0;m<n;m++)
{
temp = FIND(i,j,k,m);

if(temp > 0) pos++;
else if(temp<0) neg++;
}

if(!neg || !pos)
{
// printf("%d %d %d\n",i,j,k);
ans += area(i,j,k);
}
}

printf("Case %d: %.2lf\n",ks,ans);
}

return 0;
}