#include <bits/stdc++.h>
using namespace std;
typedef unsigned long long ull;
class person {
public:
    int angry, time;
    person(int angry, int time) {
        this->angry = angry;
        this->time = time;
    }
    ~person() {}
    bool operator<(person a) { return this->time * a.angry < this->angry * a.time; }
};

int main() {
    int n;
    cin >> n;
    vector<person> persons;
    for (int i = 0; i < n; i++) {
        int a, t;
        cin >> a >> t;
        persons.push_back(person(a, t));
    }
    sort(persons.begin(), persons.end());
    vector<ull> time;
    ull curTime = 0;
    for (auto curPerson : persons) {
        curTime += curPerson.time;
        time.push_back(curTime);
    }
    ull ans = 0;
    for (int i = 0; i < persons.size(); i++) {
        ans += persons.at(i).angry * time.at(i);
    }
    cout << ans;
}