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