#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:256000000")
using namespace std;
const int INF = 1000 * 1000 * 1000;
bool cmp(const pair<int, int> &lp, const pair<int, int> &rp) {
  return lp.first * (100.0 - rp.first) * lp.second >
         rp.first * (100.0 - lp.first) * rp.second;
}
int main() {
  int N;
  scanf("%d", &N);
  vector<pair<int, int> > v(N);
  for (int i = (0); i < (N); ++i) {
    scanf("%d%d", &v[i].second, &v[i].first);
  }
  sort(v.begin(), v.end(), cmp);
  double res = v[0].second;
  double M = v[0].first / 100.0 * v[0].second;
  for (int i = (1); i < (N); ++i) {
    res += v[i].second;
    res += (100 - v[i].first) / 100.0 * M;
    M += v[i].first / 100.0 * v[i].second;
  }
  printf("%.11lf", res);
  return 0;
}
