#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <unordered_map>
#include <utility>
#define x first
#define y second
typedef long long ll;
using namespace std;
typedef pair<int, int> PII;
const int N = 1e5 + 100;

vector<PII> v;
ll pre[N];

bool cmp(PII a, PII b) { a.y* b.x < a.x* b.y; }

int main() {
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        int a, b;
        cin >> a >> b;
        v.push_back(make_pair(a, b));
    }
    sort(v.begin(), v.end(), cmp);
    ll res = 0;
    for (int i = 0; i < v.size(); i++) {
        if (i == 0)
            pre[i] = v[i].y;
        else
            pre[i] = pre[i - 1] + v[i].y;
        res += v[i].x * pre[i];
    }
    printf("%lld\n", res);

    return 0;
}