#include <bits/stdc++.h>
using namespace std;
struct Song {
  int l, p;
  bool operator<(const Song &q) const {
    return l * p * (100 - q.p) > q.l * q.p * (100 - p);
  }
};
int main() {
  vector<Song> v;
  int n, i;
  long long ans = 0;
  scanf("%d", &n);
  v.resize(n);
  for (i = 0; i < n; i++) scanf("%d%d", &v[i].l, &v[i].p);
  stable_sort(v.begin(), v.end());
  long long qsum = 0;
  for (i = n - 1; i >= 0; i--) {
    ans += v[i].l * (10000 + v[i].p * qsum);
    qsum += 100 - v[i].p;
  }
  printf("%I64d.%04I64d\n", ans / 10000, ans % 10000);
  return 0;
}
