#include <bits/stdc++.h>
using namespace std;
int n;
double P[50010];
struct Node {
  double l, p;
  Node() {}
  Node(int a, int b) { l = a, p = b / 100.0; }
  bool operator<(const Node tmp) const {
    return p * l * (1.0 - tmp.p) - tmp.p * tmp.l * (1.0 - p) > 0;
  }
} node[50010];
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    node[i] = Node(a, b);
  }
  sort(node + 1, node + n + 1);
  for (int i = n; i >= 1; i--) P[i] = P[i + 1] + (1.0 - node[i].p);
  double ans = 0.0;
  for (int i = 1; i <= n; i++)
    ans += node[i].p * node[i].l * P[i + 1] + node[i].l;
  printf("%.9lf\n", ans);
  return 0;
}
