#include <bits/stdc++.h>
using namespace std;
const int N = 50 * 1000 + 100;
int n;
pair<long double, long double> a[N];
long double eg;
long double et;
bool cmp(pair<long double, long double> u, pair<long double, long double> v) {
  if (u.first * u.second * (1 - v.second) > v.first * v.second * (1 - u.second))
    return true;
  return false;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (int i = 0; i < n; ++i) {
    cin >> a[i].first >> a[i].second;
    a[i].second /= 100;
  }
  sort(a, a + n, cmp);
  for (int i = 1; i <= n; ++i) {
    et = et + a[i - 1].first + eg * (1. - a[i - 1].second);
    eg = eg + a[i - 1].first * a[i - 1].second;
  }
  cout << fixed << setprecision(9) << et << "\n";
  return 0;
}
