#include <bits/stdc++.h>

#pragma GCC optimize("O3")
#define int long long

using namespace std;

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

signed main(){
	cin.tie(0);
	ios::sync_with_stdio(0);
	int n;
	cin >> n;
	vector<pair<int,int>> a(n);
	for(int i = 0; i < n; i++) cin >> a[i].first >> a[i].second;
	int v = 0, d = 0;
	for(int i = 0; i < n; i++){
		d += 2*v*a[i].second + a[i].first*a[i].second*a[i].second;
		v += a[i].first * a[i].second;
	}
	int norm = d;
	for(int i = 0; i < n; i++) a[i].second = -a[i].second;
	sort(a.rbegin(),a.rend());
	for(int i = 0; i < n; i++) a[i].second = -a[i].second;
	v = 0, d = 0;
	for(int i = 0; i < n; i++){
		d += 2*v*a[i].second + a[i].first*a[i].second*a[i].second;
		v += a[i].first * a[i].second;
	}
	int opt = d;
	cout << (opt-norm)/2 << "." << 5*((opt-norm)%2) << "\n";
}