#include <bits/stdc++.h>
using namespace std;
struct song {
  int l, p;
  friend bool operator<(song a, song b) {
    return a.l * a.p * (100 - b.p) > b.l * b.p * (100 - a.p);
  }
};
song a[50005];
double R, liked;
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; ++i) {
    cin >> a[i].l >> a[i].p;
    R += a[i].l;
  }
  sort(a, a + n);
  for (int i = 0; i < n; ++i) {
    double pp = double(a[i].p) / 100.;
    R += liked * (1 - pp);
    liked += a[i].l * pp;
  }
  cout << fixed << setprecision(12) << R;
  return 0;
}
