#include <bits/stdc++.h>
using namespace std;
int N;
struct Node {
  double p;
  int l;
  double s, e;
  Node() {}
  Node(int pp, int ll) : l(ll) {
    this->p = (double)pp / 100.0;
    if (pp < 100) {
      this->s = l * p / (1 - p);
    }
  }
  bool operator<(const Node& x) const {
    if (this->p == 1 || x.p == 1) {
      return this->p == 1;
    }
    return this->s > x.s;
  }
};
Node nodes[550000];
int main() {
  cin >> N;
  int len, p;
  for (int i = 0; i < N; i++) {
    cin >> len >> p;
    nodes[i] = Node(p, len);
  }
  sort(nodes, nodes + N);
  nodes[0].e = nodes[0].p * nodes[0].l;
  for (int i = 1; i < N; i++) {
    nodes[i].e = nodes[i - 1].e + nodes[i].p * nodes[i].l;
  }
  double ans = nodes[0].l;
  for (int i = 1; i < N; i++) {
    ans += nodes[i].p * nodes[i].l +
           (1 - nodes[i].p) * (nodes[i].l + nodes[i - 1].e);
  }
  printf("%.9lf\n", ans);
  return 0;
}
