#include <bits/stdc++.h>
using namespace std;
pair<int, int> a[50001];
int s[50001];
int cmp(const pair<int, int> &a, const pair<int, int> &b) {
  return a.first * a.second * (100 - b.first) <
         b.first * b.second * (100 - a.first);
}
int main() {
  int n, i;
  scanf("%d", &n);
  for (i = 0; i < n; i++) {
    int l, p;
    scanf("%d%d", &l, &p);
    a[i] = make_pair(p, l);
  }
  sort(a, a + n, &cmp);
  reverse(a, a + n);
  for (i = n - 2; i >= 0; i--) s[i] = s[i + 1] + (100 - a[i + 1].first);
  double ans = 0;
  for (i = 0; i < n; i++)
    ans += a[i].second * (1 + a[i].first / 100. * s[i] / 100.);
  printf("%.10lf\n", ans);
  return 0;
}
