#include <bits/stdc++.h>
using namespace std;
int l[50000];
int p[50000];
pair<pair<double, int>, int> prod[50000];
int main() {
  std::ios_base::sync_with_stdio(false);
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> l[i] >> p[i];
    if (p[i] == 100)
      prod[i].first.first = -1000000000;
    else
      prod[i].first.first = -l[i] * p[i] * 1.0 / (100 - p[i]);
    prod[i].first.second = p[i];
    prod[i].second = i;
  }
  sort(prod, prod + n);
  double F = l[prod[0].second] * p[prod[0].second] / 100.0;
  double E = l[prod[0].second];
  for (int i = 1; i < n; i++) {
    E = E + l[prod[i].second] + (1 - p[prod[i].second] / 100.0) * F;
    F += p[prod[i].second] / 100.0 * l[prod[i].second];
  }
  cout << setprecision(25) << E << endl;
  return 0;
}
