#include<cstdio>

#include<cmath>

#include<algorithm>

#include<cstring>

using namespace std;

#define N 3002

typedef double db;

typedef long long ll;

struct Point{ll x,y;db jiao;}p[N],v[N];

int n;

ll sumx[N],sumy[N],ans;

bool cmp(const Point &a,const Point &b){return a.y<b.y;}

bool cmp2(const Point &a,const Point &b){return a.jiao<b.jiao;}

int main()

{

	scanf("%d",&n);

	for(int i=1;i<=n;++i)

	  scanf("%lld%lld",&p[i].x,&p[i].y);

	sort(p+1,p+n+1,cmp);

	for(int i=1;i<=n-2;++i)

	  {

	  	for(int j=i+1;j<=n;++j)

	  	  {

	  	  	v[j].x=p[j].x-p[i].x;

	  	  	v[j].y=p[j].y-p[i].y;

	  	  	v[j].jiao=atan2((db)v[j].y,(db)v[j].x);

	  	  }

	  	sort(v+i+1,v+n+1,cmp2);

	  	for(int j=n;j>i;--j)

	  	  {

	  	  	sumx[j]=sumx[j+1]+v[j].x;

	  	  	sumy[j]=sumy[j+1]+v[j].y;

	  	  }

	  	for(int j=i+1;j<n;++j)

	  	  ans+=(v[j].x*sumy[j+1]-v[j].y*sumx[j+1]);

	  }

    printf("%lld",ans>>1);

    if(ans&1) puts(".5");

	else puts(".0");

	return 0;

}