#include <bits/stdc++.h>
using namespace std;
vector<pair<int, int> > v;
bool cmp(pair<int, int> a, pair<int, int> b) {
  return a.first * a.second * (100 - b.first) >
         b.first * b.second * (100 - a.first);
}
int main() {
  int n, l, p, i, j;
  double val = 0, ans = 0;
  scanf("%d", &n);
  for (i = 1; i <= n; i++) {
    scanf("%d %d", &l, &p);
    v.push_back({p, l});
  }
  sort(v.begin(), v.end(), cmp);
  for (i = 0; i < v.size(); i++) {
    ans += (double)v[i].second;
    ans += val * (double)(100 - v[i].first) / 100;
    val += ((double)v[i].second * (double)v[i].first) / 100;
  }
  printf("%.9lf", ans);
}
