#include <bits/stdc++.h>
long double _ld;
using namespace std;
int n, m;
int i, j, k, l;
pair<int, int> p[111111];
bool cmp(pair<int, int> s1, pair<int, int> s2) {
  int p1 = s1.first;
  int l1 = s1.second;
  int p2 = s2.first;
  int l2 = s2.second;
  return l1 * (100 - p2) * p1 > l2 * (100 - p1) * p2;
}
int main() {
  cin >> n;
  for (i = 0; i < n; ++i) {
    int ll, pp;
    cin >> ll >> pp;
    p[i] = make_pair(pp, ll);
  }
  sort(p, p + n, cmp);
  typeof(_ld) el = 0;
  typeof(_ld) et = 0;
  for (i = 0; i < n; ++i) {
    typeof(_ld) pr = (typeof(_ld))p[i].first / 100;
    int len = p[i].second;
    et = pr * (et + len) + (1 - pr) * (et + el + len);
    el = el + pr * len;
  }
  printf("%.15lf\n", (double)et);
  return 0;
}
