#include <bits/stdc++.h>
using namespace std;
const int N = 110;
int t[N], d[N];
struct Node {
    int id;//第几只兔子
    int t;//跑一趟的消耗时间
    int d;//破坏力
    bool operator<(const Node &b) const {
        return d * 1.0 / t > b.d * 1.0 / b.t;
    }
} a[N];

/*
6
3 1
2 5
2 3
3 2
4 1
1 6
 */
int main() {
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) cin >> a[i].t >> a[i].d, a[i].id = i;
    sort(a + 1, a + n + 1);

    // for (int i = 1; i <= n; i++) cout << a[i].id << " ";

    // 计算破坏了多少花卉
    int sum = 0;
    for (int i = 1; i < n; i++)
        for (int j = i + 1; j <= n; j++)
            sum += a[j].d * a[i].t * 2;

    cout << sum << endl;
    return 0;
}