#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-9;
const double PI = acos(-1.0);
const long long int mod = 1e9 + 7;
const int MAXN = 1e6 + 5;
int n;
vector<pair<int, int> > arr;
void cp() {
  cin >> n;
  arr.resize(n);
  for (int i = 0, l, p; i < n; i++) cin >> arr[i].first >> arr[i].second;
  sort(arr.begin(), arr.end(), [&](pair<int, int> a, pair<int, int> b) {
    double pa = a.second / 100.0;
    double push_back = b.second / 100.0;
    return a.first * pa / (1 - pa) > b.first * push_back / (1 - push_back);
  });
  long double pref = 0, ans = 0;
  for (int i = 0; i < n; i++) {
    long double p = arr[i].second / 100.0;
    long double len = arr[i].first;
    ans += pref * (1 - p);
    ans += len;
    pref += len * p;
  }
  cout << setprecision(10) << fixed;
  ;
  cout << ans << '\n';
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  int t;
  t = 1;
  while (t--) {
    cp();
  }
  return 0;
}
