#include <bits/stdc++.h>
#pragma comment(linker, "/Stack:64000000")
using namespace std;
const int N = 50005;
void qsort(int *l, double *p, int first, int last) {
  int left = first, right = last;
  double v =
      l[(left + last) / 2] * p[(left + last) / 2] / (1 - p[(left + last) / 2]);
  while (left <= right) {
    while (l[left] * p[left] / (1 - p[left]) > v) ++left;
    while (l[right] * p[right] / (1 - p[right]) < v) --right;
    if (left <= right) {
      swap(l[left], l[right]);
      swap(p[left], p[right]);
      ++left;
      --right;
    }
  }
  if (left < last) qsort(l, p, left, last);
  if (first < right) qsort(l, p, first, right);
}
int main() {
  int n;
  cin >> n;
  int l[N];
  double p[N];
  for (int i = 0; i < n; ++i) {
    cin >> l[i] >> p[i];
    p[i] /= 100;
  }
  qsort(l, p, 0, n - 1);
  double s[N];
  s[0] = 1 - p[0];
  for (int i = 1; i < n; ++i) s[i] = s[i - 1] + 1 - p[i];
  double c = 0;
  for (int i = 0; i < n; ++i) c += l[i] * (1 + p[i] * (s[n - 1] - s[i]));
  cout.setf(ios::fixed);
  cout.precision(9);
  cout << c << '\n';
}
