#include <bits/stdc++.h>
using namespace std;
struct node {
	int t, d;
	double flag;
}a[105];
int cmp(node x, node y) {
	return x.flag < y.flag;
}
double n, sum;
signed main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> a[i].t >> a[i].d;
		a[i].flag = a[i].t / a[i].d;
	}
	sort(a, a + n, cmp);
	for (int i = 0; i < (n - 1); i++) {
		for (int j = i + 1; j < n; j++)
			sum += (2 * a[i].t * a[j].d);
	}
	cout << sum;
	return 0;
}