#include <bits/stdc++.h>
using namespace std;
template <class T>
void read(T& container) {
  for (typename T::value_type& x : container) cin >> x;
}
template <class T>
void print(T& container, const char separator = ' ') {
  for (typename T::value_type& x : container) cout << x << separator;
}
void openFiles(const char* in, const char* out) {
  freopen(in, "r", stdin);
  freopen(out, "w", stdout);
}
void run() {
  int n;
  cin >> n;
  vector<pair<double, double> > v(n);
  for (pair<double, double>& p : v) {
    cin >> p.first >> p.second;
    p.second /= 100;
  }
  sort(v.begin(), v.end(),
       [](pair<double, double> p1, pair<double, double> p2) {
         return p1.first * p1.second * (1 - p2.second) >
                p2.first * p2.second * (1 - p1.second);
       });
  double prod = v[0].first * v[0].second, res = v[0].first;
  for (int i = 1; i < n; ++i) {
    res += v[i].first + (1 - v[i].second) * prod;
    prod += v[i].first * v[i].second;
  }
  printf("%.10lf\n", res);
}
int main() {
  run();
  return 0;
}
