#include <bits/stdc++.h>
using namespace std;
pair<long double, pair<long double, long double> > arr[100005];
long long n;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (int i = 1; i <= n; ++i) {
    cin >> arr[i].second.first >> arr[i].second.second;
    arr[i].second.second /= 100.0;
    arr[i].first = arr[i].second.first * arr[i].second.second;
    if (arr[i].second.second == 1) {
      arr[i].first = 1000000009;
    } else
      arr[i].first /= (1.0 - arr[i].second.second);
  }
  sort(arr + 1, arr + n + 1);
  reverse(arr + 1, arr + n + 1);
  long double tmp = 0;
  long double anse = 0;
  for (int i = 1; i <= n; ++i) {
    anse += arr[i].second.first;
    anse += ((1.000000 - (arr[i].second.second)) * (tmp));
    tmp += ((arr[i].second.second) * arr[i].second.first);
  }
  cout << showpoint << setprecision(14) << anse;
  return 0;
}
