#include <iostream>

#include <vector>

#include <cstdio>

#include <cstring>

#include <algorithm>

#include <cmath>

#include <map>

#include <set>

#include <string>

#include <queue>

#include <stack>

#include <bitset>

using namespace std;

#define pb(x) push_back(x)

#define ll long long

#define mk(x, y) make_pair(x, y)

#define lson l, m, rt<<1

#define mem(a) memset(a, 0, sizeof(a))

#define rson m+1, r, rt<<1|1

#define mem1(a) memset(a, -1, sizeof(a))

#define mem2(a) memset(a, 0x3f, sizeof(a))

#define rep(i, n, a) for(int i = a; i<n; i++)

#define fi first

#define se second

typedef pair<int, int> pll;

const double PI = acos(-1.0);

const double eps = 1e-;

const int mod = 1e9+;

const int inf = ;

const int dir[][] = { {-, }, {, }, {, -}, {, } };

const int maxn = ;

struct point

{

    int x,y;

};

point a[maxn];

int st[maxn], top;

int cross(point p0,point p1,point p2)

{

    return (p1.x-p0.x)*(p2.y-p0.y)-(p1.y-p0.y)*(p2.x-p0.x);

}

double dis(point p1,point p2)

{

    return sqrt((double)(p2.x-p1.x)*(p2.x-p1.x)+(p2.y-p1.y)*(p2.y-p1.y));

}

bool cmp(point p1,point p2)

{

    int tmp=cross(a[],p1,p2);

    if(tmp>) return true;

    else if(tmp==&&dis(a[],p1)<dis(a[],p2)) return true;

    else return false;

}

void init(int n)

{

    int i,k;

    point p0;

    scanf("%d%d",&a[].x,&a[].y);

    p0.x=a[].x;

    p0.y=a[].y;

    k=;

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

    {

        scanf("%d%d",&a[i].x,&a[i].y);

        if( (p0.y>a[i].y) || ((p0.y==a[i].y)&&(p0.x>a[i].x)) )

        {

            p0.x=a[i].x;

            p0.y=a[i].y;

            k=i;

        }

    }

    a[k]=a[];

    a[]=p0;

    sort(a+,a+n,cmp);

}

void graham(int n)

{

    int i;

    if(n==) {top=;st[]=;}

    if(n==)

    {

        top=;

        st[]=;

        st[]=;

    }

    if(n>)

    {

        for(i=;i<=;i++) st[i]=i;

        top=;

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

        {

            while(top>&&cross(a[st[top-]],a[st[top]],a[i])<=) top--;

            top++;

            st[top]=i;

        }

    }

}

int main()

{

    int n, r;

    while(cin>>n) {

        init(n);

        graham(n);

        double ans = ;

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

            ans += (a[st[i]].x*a[st[i+]].y-a[st[i]].y*a[st[i+]].x);

        }

        ans += a[st[top]].x*a[st[]].y-a[st[top]].y*a[st[]].x;

        ans /= ;

        cout<<int(ans/)<<endl;

    }

    return ;

}