#include<iostream>#include<cstdio>#include<cstring>#include<queue>#include<vector>#include<map>#include<set>#include<cmath>#include<complex>#include<algorithm>#define EPS 1e-10#define largty(x,y) (x-EPS)>(y)#define smalty(x,y) (x+EPS)<(y)#define nlargty(x,y) (x-EPS)<(y)#define nsmalty(x,y) (x+EPS)>(y)#define equal(x,y) (nlargty(x,y) && (nsmalt(x,y)))#define max(a,b) (a)>(b)?(a):(b)#define min(a,b) (a)<(b)?(a):(b)#define MAXN 50004using namespace std;struct point { double x, y; point(){} point(double _x, double _y):x(_x),y(_y){} point(const point &temp) { x = temp.x; y = temp.y; }}data[MAXN],convex[MAXN];point start(0,0);inline double cross(const point &p1, const point &p2, const point &q1, const point &q2){ return (q2.y - q1.y)*(p2.x - p1.x) - (q2.x - q1.x)*(p2.y - p1.y); }inline bool cmp1(const point &a, const point &b){ return a.y < b.y || (a.y == b.y && a.x < b.x); }inline bool cmp2(const point &a, const point &b)//逆时针排序 { point origin; origin = start; return cross(origin,a,origin,b) > 0 || (cross(origin,a,origin,b) == 0 && fabs(a.x) < fabs(b.x));}inline void convex_hull(int &cnt, int n){ sort(data,data+n,cmp1); start = data[0]; sort(data+1,data+n,cmp2); convex[cnt++] = start; convex[cnt++] = data[1]; for (int i(2); i<n; ++i) { while (cnt >= 2 && cross(convex[cnt-2],convex[cnt-1],convex[cnt-1],data[i]) <= 0)--cnt; convex[cnt++] = data[i]; } }inline double rotating_calipers(int n){ int j = 1,k = 0; double area(0); for (int i(0); i<n; ++i) { j = (i + 1)%n; k = (j + 1)%n; while (fabs(cross(convex[i],convex[j],convex[i],convex[k])) < fabs(cross(convex[i],convex[j],convex[i],convex[(k+1)%n]))) { k = (k + 1)%n; } while (j != i && k != i) { area = max(area,fabs(cross(convex[i],convex[j],convex[i],convex[k]))); while (fabs(cross(convex[i],convex[j],convex[i],convex[k])) < fabs(cross(convex[i],convex[j],convex[i],convex[(k+1)%n]))) { k = (k + 1)%n; } j = (j + 1)%n; } } return area; }int main(){ int n; while (scanf("%d",&n) && n != -1) { for (int i(0); i<n; ++i) { scanf("%lf%lf",&data[i].x,&data[i].y); } if (n <= 2) { cout<<"0.00"<<endl; continue; } int cnt(0); convex_hull(cnt,n); if (cnt <= 2) { cout<<"0.00"<<endl; continue; } else { if (cnt == 3) { printf("%.2lfn",fabs(cross(convex[0],convex[1],convex[0],convex[2]))/2); } else { printf("%.2lfn",rotating_calipers(cnt)/2); } } } return 0; }
