#include <bits/stdc++.h>
const double pi = acos(-1.0);
using namespace std;
struct data {
  double l, p;
  double calc() const { return l * p / (100 - p); }
  bool operator<(const data &b) const { return calc() > b.calc(); }
};
int N, i;
double s, ans;
data a[51000];
int main() {
  cin >> N;
  for (i = 0; i < N; i++) cin >> a[i].l >> a[i].p;
  sort(a, a + N);
  for (i = 0; i < N; i++) {
    double l = a[i].l, p = a[i].p / 100;
    ans += l + s * (1 - p);
    s += l * p;
  }
  printf("%.15lf\n", ans);
}
