Rectangular Pasture

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

struct Coor{
    ll x, y;
    ll nx, ny;
    //bool operator<(const Coor &a) const{
        //if(y==a.y){
            //return x<a.x;
        //}
        //return y<a.y;
    //}
};

ll n;
vector<Coor> cd;
vector<vector<ll>> pfs;
ll ans;

bool comp1(Coor a, Coor b){
    if(a.y==b.y){
        return a.x<a.y;
    }
    return a.y<b.y;
}

bool comp2(Coor a, Coor b){
    if(a.x==b.x){
        return a.y<b.y;
    }
    return a.x<b.x;
}

int main(){
    //freopen("rectangular.in", "r", stdin);

    cin >> n;
    cd.resize(n+1);
    pfs.resize(n+1, vector<ll>(n+1, 0));
    for(ll i=1; i<=n; i++){
        cin >> cd[i].x >> cd[i].y;
    }
    sort(cd.begin(), cd.end(), comp2);
    for(ll i=1; i<=n; i++){
        //cout << cd[i].x << ", " << cd[i].y << '\n';
        cd[i].nx = i;
    }
    sort(cd.begin(), cd.end(), comp1);
    for(ll i=1; i<=n; i++){
        //cout << cd[i].x << ", " << cd[i].y << '\n';
        cd[i].ny = i;
        //cout << cd[i].nx << ", " << cd[i].ny << '\n';
        pfs[cd[i].nx][cd[i].ny]++;
    }
    for(ll i=1; i<=n; i++){
        for(ll j=1; j<=n; j++){
            pfs[i][j] = pfs[i][j]+pfs[i-1][j]+pfs[i][j-1]-pfs[i-1][j-1];
            //cout << pfs[i][j] << " ";
        }
        //cout << '\n';
    }
    for(ll i=1; i<=n; i++){
        for(ll j=i+1; j<=n; j++){
            ll x1 = cd[i].nx;
            ll y1 = cd[i].ny;
            ll x2 = cd[j].nx;
            ll y2 = cd[j].ny;
            ll mnx = min(x1, x2);
            ll mny = min(y1, y2);
            ll mxx = max(x1, x2);
            ll mxy = max(y1, y2);
            ll size_left = pfs[mxx][mny]-pfs[mxx][0]-pfs[mnx-1][mny]+pfs[0][mny-1];
            ll size_right = pfs[mxx][n]-pfs[mxx][mxy-1]-pfs[mnx-1][n]+pfs[mnx-1][mxy-1];
            //cout << "mn: " << mnx << ", " << mny << '\n';
            //cout << "mx: " << mxx << ", " << mxy << '\n';
            //cout << "size_left: " << size_left << ", size_right: " << size_right << '\n';
            //cout << "size_right: " << size_right <<
            ans+=(size_left*size_right);
        }
    }
    cout << ans+n+1 << '\n';

    return 0;
}