#include <bits/stdc++.h>
using namespace std;
pair<int, int> p[100005];
int n;
void read() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) scanf("%d %d", &p[i].first, &p[i].second);
  return;
}
bool cmp(pair<int, int> a, pair<int, int> b) {
  return (a.first * a.second * (100 - b.second)) >
         (b.first * b.second * (100 - a.second));
}
void solve() {
  double cvp, t;
  int i;
  cvp = 0.0;
  t = 100;
  sort(p + 1, p + n + 1, cmp);
  for (i = n; i >= 1; i--) {
    cvp += (p[i].first * (100 - p[i].second));
    cvp += (p[i].first * p[i].second * (t / 100.0));
    t += 100 - p[i].second;
  }
  printf("%llf\n", cvp / 100.0);
  return;
}
int main() {
  read();
  solve();
}
