#include <bits/stdc++.h>
using namespace std;
const double PI = acos(-1.0);
const int MAXN = 60000;
const long long big = 1e18;
double loved = 0, answer = 0;
long long n;
pair<double, pair<double, double> > p[MAXN];
int main() {
  cin >> n;
  for (int i = 1; i <= n; ++i) {
    cin >> p[i].second.first >> p[i].second.second;
    p[i].second.second /= 100.0;
    p[i].first = -p[i].second.first * p[i].second.second;
    if (p[i].second.second < 1) {
      p[i].first /= (1 - p[i].second.second);
    } else {
      p[i].first = -big;
    }
  }
  sort(p + 1, p + 1 + n);
  for (int i = 1; i <= n; ++i) {
    answer += p[i].second.first;
    answer += loved * (1 - p[i].second.second);
    loved += p[i].second.first * p[i].second.second;
  }
  printf("%.9f", answer);
  return 0;
}
