#include <bits/stdc++.h>
using namespace std;
struct song {
  double l, p;
};
int main() {
  int n;
  cin >> n;
  vector<song> v(n);
  for (song& s : v) {
    cin >> s.l >> s.p;
    s.p /= 100;
  }
  sort(v.begin(), v.end(), [](song s1, song s2) {
    return s1.l * s1.p * (1 - s2.p) > s2.l * s2.p * (1 - s1.p);
  });
  double mu = 0, res = 0;
  for (song s : v) {
    res += s.l + (1 - s.p) * mu;
    mu += s.l * s.p;
  }
  printf("%.9lf\n", res);
  return 0;
}
