#include <bits/stdc++.h>
using namespace std;
const int maxn = 100 * 1000 + 10;
pair<int, long double> song[maxn];
int n;
long double ans, sum;
inline bool cmp(const pair<int, long double> &a,
                const pair<int, long double> &b) {
  return ((long double)1 - a.second) * b.second * b.first <
         ((long double)1 - b.second) * a.second * a.first;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> song[i].first >> song[i].second;
    song[i].second *= (long double)0.01;
  }
  sort(song, song + n, cmp);
  for (int i = 0; i < n; i++) {
    ans += song[i].first;
    ans += ((long double)1 - song[i].second) * sum;
    sum += song[i].second * (long double)song[i].first;
  }
  cout << setprecision(12) << fixed << ans;
  return 0;
}
