#include <bits/stdc++.h>
using namespace std;
bool cmp(pair<int, int> &a, pair<int, int> &b) {
  if (a.second == 100) {
    if (b.second == 100)
      return a.first < b.first;
    else
      return 1;
  }
  if (b.second == 100) return 0;
  return a.second * a.first * (100 - b.second) >
         b.second * b.first * (100 - a.second);
}
int main() {
  int n;
  scanf("%d", &n);
  vector<pair<int, int> > a(n);
  for (int i = 0; i < n; i++) scanf("%d%d", &a[i].first, &a[i].second);
  sort(a.begin(), a.end(), cmp);
  double exp = 0;
  double ans = 0;
  for (int i = 0; i < n; i++) {
    ans += a[i].first;
    ans += exp * (1 - (double)a[i].second / 100.0);
    exp += a[i].first * ((double)a[i].second / 100);
  }
  printf("%.10lf\n", ans);
  return 0;
}
