#include <bits/stdc++.h>
using namespace std;
pair<int, int> a[100010];
int main() {
  ios::sync_with_stdio(false);
  cout.setf(ios::fixed);
  cout.precision(20);
  int n;
  scanf("%d", &n);
  double like = 0, ans = 0;
  for (int i = (1); i <= (n); ++i) {
    int x, y;
    scanf("%d%d", &x, &y);
    a[i].first = x, a[i].second = y;
  }
  sort(a + 1, a + 1 + n, [](pair<int, int> a, pair<int, int> b) {
    double l = 0, r = 0;
    if (a.second == 100)
      l = 2139062143;
    else {
      l = 1.0 * a.first * a.second / (100 - a.second);
    }
    if (b.second == 100)
      r = 2139062143;
    else {
      r = 1.0 * b.first * b.second / (100 - b.second);
    }
    return l > r;
  });
  for (int i = (1); i <= (n); ++i) {
    ans += 1.0 * like * (100 - a[i].second) / 100 + a[i].first;
    like += 1.0 * a[i].first * a[i].second / 100;
  }
  printf("%.9lf\n", ans);
  return 0;
}
