#include <bits/stdc++.h>
using namespace std;
const int N = 5e4 + 4;
int n;
double res, s;
pair<int, double> a[N];
bool cmp(pair<int, double> a, pair<int, double> b) {
  return (1 - b.second) * a.first * a.second >
         (1 - a.second) * b.first * b.second;
}
int main() {
  scanf("%d", &n);
  for (int i = 0, t; i < n; ++i) {
    scanf("%d%d", &a[i].first, &t);
    a[i].second = 0.01 * t;
  }
  sort(a, a + n, cmp);
  for (int i = 0; i < n; ++i) {
    res += a[i].first + (1 - a[i].second) * s;
    s += a[i].second * a[i].first;
  }
  printf("%.10f\n", res);
}
