TIOJ 1280

#include <bits/stdc++.h>
using namespace std;
#define pii pair<int,int>
#define x first
#define y second

bool cross(pii a, pii o, pii b){
    return (o.x-a.x) * (b.y-o.y) >= (o.y-a.y) * (b.x-o.x);
}

int cac(pii a, pii o, pii b){
    return abs((o.x-a.x) * (b.y-o.y) - (o.y-a.y) * (b.x-o.x));
}

int main(){
    int n;
    pii dots[10000];
    cin >> n;
    for(int i = 0; i < n; ++i)cin >> dots[i].x >> dots[i].y;
    vector<pii> v;
    sort(dots, dots+n);
    for(int i = 0; i < n; ++i){
        while(v.size() >= 2 && cross(v[v.size()-2], v[v.size()-1], dots[i]))v.pop_back();
        v.emplace_back(dots[i]);
    }
    v.pop_back();
    int t = v.size();
    for(int i = n-1; i >= 0; --i){
        while(v.size() >= t+2 && cross(v[v.size()-2], v.back(), dots[i]))v.pop_back();
        v.emplace_back(dots[i]);
    }
    v.pop_back();
    double ans = 0;
    for(unsigned int i = 2; i < v.size(); ++i){
        ans += cac(v[0], v[i-1], v[i]);
    }
    cout << (int)(ans+1)/2 << '\n';
    return 0;
}