#include <bits/stdc++.h>
using namespace std;
double f(pair<int, int> &a) {
  return double(a.second) / (100 - a.second) * a.first;
}
bool cmp(pair<int, int> &a, pair<int, int> &b) { return f(a) > f(b); }
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int N, i;
  cin >> N;
  vector<pair<int, int> > L(N);
  vector<double> E(N + 1), Pre(N + 1, 0);
  for (i = 0; i < N; ++i) cin >> L[i].first >> L[i].second;
  sort(L.begin(), L.end(), cmp);
  for (i = 0; i < N; ++i)
    Pre[i] =
        L[i].first * 1.0 * (L[i].second / 100.0) + (i > 0 ? Pre[i - 1] : 0);
  E[0] = 0;
  E[1] = L[0].first;
  for (i = 2; i <= N; ++i)
    E[i] =
        E[i - 1] + L[i - 1].first + (1 - L[i - 1].second / 100.) * Pre[i - 2];
  cout.precision(11);
  cout << fixed << E[N];
  return 0;
}
