#include <iostream>
#include <bits/stdc++.h>

using namespace std;

bool comp(long long a, long long b) {
    return a < b;
}

void quick_sort(long long *vector, int first, int last) {
    long long mid;
    int f = first, l = last;
    mid = vector[(f + l) / 2];
    do {
        while (comp(vector[f], mid)) f++;
        while (comp(mid, vector[l])) l--;
        if (f <= l)
        {
            swap(vector[f], vector[l]);
            f++;
            l--;
        }
    } while (f < l);
    if (first < l) quick_sort(vector, first, l);
    if (f < last) quick_sort(vector, f, last);
}

int main() {
    long long n;
    cin >> n;
    long long x_s[n];
    long long y_s[n];
    long long sum = 0;
    for (long long i = 0; i < n; ++i) {
        cin >> x_s[i] >> y_s[i];
    }

    quick_sort(x_s,0,n-1);
    quick_sort(y_s,0,n-1);

//    sort(x_s, x_s + n, comp);
//    sort(y_s, y_s + n, comp);

    for (long long i = 0; i < n - 1; ++i) {
        sum += (x_s[i + 1] - x_s[i]) * (i + 1) * (n - i - 1);
        sum += (y_s[i + 1] - y_s[i]) * (i + 1) * (n - i - 1);
    }

    sum = 2 * sum / (n * (n - 1));
    cout << sum;
    return 0;
}