#include <iostream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <queue>
#include <algorithm>
using namespace std;
const int maxn = 1e5 + 5;
typedef long long ll;
struct node {
    ll a, b;
    bool operator<(const node &tmp) const {
        return tmp.a * b < a * tmp.b || (tmp.a * b == a * tmp.b && a < tmp.a);
    }
} x[maxn];
int main() {
    // freopen("1.in","r",stdin);
    // 22freopen("1.out","w",stdout);100
    int n;
    while (~scanf("%d", &n)) {
        for (int i = 1; i <= n; i++) {
            scanf("%lld%lld", &x[i].a, &x[i].b);
        }
        sort(x + 1, x + 1 + n);
        ll pre = 0, ans = 0;
        for (int i = 1; i <= n; i++) {
            pre = pre + x[i].b;
            ans = ans + pre * x[i].a;
        }
        printf("%lld\n", ans);
    }
    return 0;
}