#include <bits/stdc++.h>
using namespace std;
const int maxn = 50550;
struct Node {
  double p, l;
  bool operator<(const Node& rhs) const {
    return (1 - rhs.p) * p * l > (1 - p) * rhs.p * rhs.l;
  }
} T[maxn];
int main() {
  int n;
  cin >> n;
  double sum = 0;
  for (int i = 1; i <= n; i++) {
    int l, p;
    scanf("%d %d", &l, &p);
    T[i].l = l;
    T[i].p = p * 1.0 / 100;
    sum += T[i].l;
  }
  sort(T + 1, T + n + 1);
  double P = 0;
  for (int i = n; i >= 1; i--) {
    sum += P * T[i].p * T[i].l;
    P += 1 - T[i].p;
  }
  printf("%.9lf\n", sum);
}
