#include <cstdio>

 #include <cmath>

 #include <algorithm>

 #include <vector>

 using namespace std;

 typedef double db;

 const db eps=1e-;

 const db pi=acos(-);

 int sign(db k){

     if (k>eps) return ; else if (k<-eps) return -; return ;

 }

 int cmp(db k1,db k2){return sign(k1-k2);}

 struct point{

     db x,y;

     point operator + (const point &k1) const{return (point){k1.x+x,k1.y+y};}

     point operator - (const point &k1) const{return (point){x-k1.x,y-k1.y};}

     point operator * (db k1) const{return (point){x*k1,y*k1};}

     point operator / (db k1) const{return (point){x/k1,y/k1};}

     bool operator == (const point &k1) const{return cmp(x,k1.x)==&&cmp(y,k1.y)==;}

     bool operator <(const point &k1)const {

         int c=cmp(x,k1.x);

         if(c)return c==-;

         return cmp(y,k1.y)==-;

     }

 };

 db cross(point k1,point k2){return k1.x*k2.y-k1.y*k2.x;}

 db dot(point k1,point k2){return k1.x*k2.x+k1.y*k2.y;}

 int n;

 vector<point> convexHull(vector<point> ps){

     int n = ps.size();if(n<=)return ps;

     sort(ps.begin(),ps.end());

     vector<point> qs(n*);int k=;

     for(int i=;i<n;qs[k++]=ps[i++])

         while (k>&&cross(qs[k-]-qs[k-],ps[i]-qs[k-])<=)--k;

     for(int i=n-,t=k;i>=;qs[k++]=ps[i--])

         while (k>t&&cross(qs[k-]-qs[k-],ps[i]-qs[k-])<=)--k;

     qs.resize(k-);

     return qs;

 }

 vector<point>p;

 db x,y;

 int main(){

     scanf("%d",&n);

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

         scanf("%lf%lf",&x,&y);

         p.push_back(point{x,y});

     }

     p=convexHull(p);

     int m=p.size();

     int ans=;

     for(int i=;i<m;i++){

         ans+=cross(p[i],p[(i+)%m]);

     }

     ans=abs(ans)/;

     printf("%d\n",ans/);

 }