#include <bits/stdc++.h>
using namespace std;
using pii = pair<int, int>;
pii p[50000];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = n; i--;) {
    scanf("%d %d", &p[i].first, &p[i].second);
  }
  sort(p + 0, p + n, [&](pii a, pii b) {
    return a.first * a.second * (100 - b.second) <
           b.first * b.second * (100 - a.second);
  });
  double ans = 0, sum = 0;
  for (int i = n; i--;) {
    ans += p[i].first + sum * (1 - p[i].second / 100.);
    sum += p[i].first * p[i].second / 100.;
  }
  printf("%.10lf\n", ans);
}
