HLCOVER - BUT STUPID

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <set>
#define task "HLCOVER"
using namespace std;
using ll = long long;
using ld = long double;

template<class T>
void read(T &x){
    register int c;
    x = 0;
    bool neg = 0;
    while((c = getchar()) && c < '0' || c > '9');
    for(; c >= '0' && c <= '9'; c = getchar())
        x = x * 10 + c - '0';
}
const int N = 5e3 + 2;
int n;
struct Point{
    ll x, y;
    Point() {}
    Point(ll u, ll v){
        x = u;
        y = v;
    }
    bool operator < (const Point &a) const{
        return x < a.x
            || (x == a.x && y < a.y);
    }
};
using TPoint = Point*;
Point a[N], b[N];
TPoint s[N];

void Read(){
    //cin >> n;
    read(n);
    for(int i = 1; i <= n; ++i){
        //cin >> a[i].x >> a[i].y;
        read(a[i].x);
        read(a[i].y);
        //a[i].x = abs(a[i].x);
        //a[i].y = abs(a[i].y);
        s[i] = &a[i];
    }
    sort(s + 1, s + n + 1, [&](TPoint &a, TPoint &b){return *a < *b;});
    for(int i = 1; i <= n; ++i)
        b[i] = *s[i];
}

bool Check(int i, int j){
    if(b[i].x <= b[j].x && b[i].y <= b[j].y)
        return true;
    ll S1 = b[i].x * b[j].y,
       S2 = (b[j].x - b[i].x) * (b[i].y - b[j].y);
    return S1 >= S2;
}

struct com{
    bool operator () (const TPoint &x, const TPoint &y) const{
        return *x < *y;
    }
};

void Solve(){
    for(int i = 1; i <= n; ++i)
        for(int j = i + 1; j <= n; ++j)
            if(b[i].x <= b[j].x && b[i].y <= b[j].y)
                b[i] = b[j] = Point(max(b[i].x, b[j].x),
                                    max(b[i].y, b[j].y));
    for(int i = 1; i <= n; ++i)
        for(int j = i + 1; j <= n; ++j)
            if(Check(i, j))
                b[i] = b[j] = Point(max(b[i].x, b[j].x),
                                    max(b[i].y, b[j].y));
    set<TPoint, com> s;
    ll ans = 0;
    for(int i = 1; i <= n; ++i)
        if(s.find(&b[i]) == s.end()){
            //cout << b[i].x << " " << b[i].y << "\n";
            ans += b[i].x * b[i].y * 4;
            s.insert(&b[i]);
        }
    cout << ans;
}

int32_t main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0); if(fopen(task".INP", "r"))
    freopen(task".INP", "r", stdin),
    freopen(task".OUT", "w", stdout);
    Read();
    Solve();
}