1 #include<stdio.h>
2 #include<math.h>
3 typedef struct dian
4 {
5 int x,y;
6 };
7 dian p[50005],ch[50005];
8 double area(int i,int j,int k)
9 {
10 double a,b,c,q;
11 a=sqrt(1.0*(ch[j].x-ch[i].x)*(ch[j].x-ch[i].x)+1.0*(ch[j].y-ch[i].y)*(ch[j].y-ch[i].y));
12 b=sqrt(1.0*(ch[k].x-ch[i].x)*(ch[k].x-ch[i].x)+1.0*(ch[k].y-ch[i].y)*(ch[k].y-ch[i].y));
13 c=sqrt(1.0*(ch[j].x-ch[k].x)*(ch[j].x-ch[k].x)+1.0*(ch[j].y-ch[k].y)*(ch[j].y-ch[k].y));
14 q=(a+b+c)/2;
15 return(sqrt(q*(q-a)*(q-b)*(q-c)));
16 }
17 int cross(dian p1,dian p2,dian p3)
18 {
19 int x1=p2.x-p1.x,y1=p2.y-p1.y;
20 int x2=p3.x-p1.x,y2=p3.y-p1.y;
21 return(x1*y2-x2*y1);
22 }
23 void sort(int l,int r)
24 {
25 int i,j,x,x1,y;
26 i=l; j=r;
27 x=p[(i+j)/2].x; x1=p[(i+j)/2].y;
28 while (i<=j)
29 {
30 while (p[i].x<x||(p[i].x==x&&p[i].y<x1)) i++;
31 while (x<p[j].x||(p[j].x==x&&x1<p[j].y)) j--;
32 if (i<=j){
33 y=p[i].x; p[i].x=p[j].x; p[j].x=y;
34 y=p[i].y; p[i].y=p[j].y; p[j].y=y;
35 i++; j--;
36 }
37 }
38 if (i<r) sort(i,r);
39 if (l<j) sort(l,j);
40 }
41 int main()
42 {
43 int n,i,sum,j,k;
44 int xx,yy,zz;
45 double max;
46 while (~scanf("%d",&n)&&n!=-1)
47 {
48 for (i=1;i<=n;i++) scanf("%d%d",&p[i].x,&p[i].y);
49
50 sort(1,n);
51 sum=1;
52 for (i=1;i<=n;i++){
53 while (sum>=3&&cross(ch[sum-2],ch[sum-1],p[i])<=0) sum--;
54 ch[sum]=p[i];
55 sum++;
56 }
57 k=sum-1;
58 for (i=n-1;i>=1;i--){
59 while (sum>=k+2&&cross(ch[sum-2],ch[sum-1],p[i])<=0) sum--;
60 ch[sum]=p[i];
61 sum++;
62 }
63 sum--;
64 // for (i=1;i<=sum;i++) printf("%d %d\n",ch[i].x,ch[i].y);
65 max=0.00;
66
67 j=3; k=2;
68 ch[sum+1]=ch[2];
69 for (i=1;i<=sum;i++)
70 {
71 // j=i+1; k=j+1;
72 while (area(i,j,k)<area(i,j,k+1)) {k++; if (k>sum) k=1; }
73 if (area(i,j,k)>max) {max=area(i,j,k);
74 xx=i; yy=j; zz=k;}
75 while (area(i,j,k)<area(i,j+1,k)) {j++; if (j>sum) j=1; }
76 if (area(i,j,k)>max) {max=area(i,j,k);
77 xx=i; yy=j; zz=k;}
78 // for (j=i+1;j<=sum-1;j++)
79 // for (k=j+1;k<=sum;k++)
80 // {
81 // if (area(i,j,k)>max) max=area(i,j,k);
82 // if (k<sum&&area(i,j,k+1)<=area(i,j,k)) break;
83 // }
84 }
85 printf("%.2lf\n",max);
86 }
87 }
