#include <bits/stdc++.h>
using namespace std;
bool cmp(pair<int, double> a, pair<int, double> b) {
  return a.first * a.second * (1 - b.second) >
         b.first * b.second * (1 - a.second);
}
int n;
pair<int, double> ar[50000];
double ans, len;
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    scanf("%d%lf", &ar[i].first, &ar[i].second);
    ar[i].second /= 100.0;
  }
  sort(ar, ar + n, cmp);
  for (int i = 0; i < n; i++) {
    ans += ar[i].first;
    ans += len * (1.0 - ar[i].second);
    len += ar[i].first * ar[i].second;
  }
  printf("%lf\n", ans);
  return 0;
}
