#include <bits/stdc++.h>
using namespace std;
int p[202000], l[202000];
int n;
int id[202000];
bool cmp(int i, int j) {
  return p[i] * l[i] / (100.0 - p[i]) > p[j] * l[j] / (100.0 - p[j]);
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; ++i) {
    scanf("%d%d", &l[i], &p[i]);
    id[i] = i;
  }
  sort(id + 1, id + n + 1, cmp);
  double ans = 0;
  double mul = 0;
  for (int i = n; i >= 1; --i) {
    int u = id[i];
    ans += l[u];
    ans += p[u] * 1.0 / 100 * l[u] * mul;
    mul += 1 - p[u] / 100.0;
  }
  printf("%.12lf\n", ans);
  return 0;
}
