#include <map>
#include <ctime>
#include <cmath>
#include <queue>
#include <stack>
#include <vector>
#include <string>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <algorithm>
#define spause() system("pause")
//#define scanf scanf_s

using namespace std;
typedef long long llong;
typedef unsigned long long ullong;
typedef pair<int, int> prdd;

int n, tpa, tpb;
llong ans = 0, tot = 0;
vector<prdd> trs;

bool cmp(prdd a, prdd b) { return a.second * b.first < a.first * b.second; }

int main() {
    scanf("%d", &n);
    for (int i = 0; i < n; i++) {
        scanf("%d%d", &tpa, &tpb);
        trs.push_back(prdd(tpa, tpb));
    }

    sort(trs.begin(), trs.end(), cmp);

    for (unsigned i = 0; i < trs.size(); i++) {
        tot += trs.at(i).second;
        ans += trs.at(i).first * tot;
    }

    printf("%lld", ans);

    // spause();
    return 0;
}