#include <bits/stdc++.h>
using namespace std;
int n;
pair<int, int> arr[100000];
bool cmp(pair<int, int> a, pair<int, int> b) {
  return (100 - b.second) * a.second * a.first >
         (100 - a.second) * b.second * b.first;
}
int main() {
  cin >> n;
  for (int i = 0; i < n; i++) cin >> arr[i].first >> arr[i].second;
  sort(arr, arr + n, cmp);
  long long res = 0;
  long long sum = 0;
  for (int i = 0; i < n; i++) {
    res += 10000 * arr[i].first + (100 - arr[i].second) * sum;
    sum += arr[i].first * arr[i].second;
  }
  cout << setprecision(6) << fixed << showpoint << (double)res / 10000 << endl;
  return 0;
}
