#include <bits/stdc++.h>
using namespace std;
const int N = 5e4 + 9;
int n;
struct node {
  int l;
  double p;
} a[N];
bool cmp(node a, node b) {
  return a.l * a.p * (1 - b.p) > b.l * b.p * (1 - a.p);
}
double p[N];
int main() {
  cin >> n;
  for (int i = 0; i < n; i++) scanf("%d%lf", &a[i].l, &a[i].p), a[i].p /= 100;
  sort(a, a + n, cmp);
  p[n - 1] = 1 - a[n - 1].p;
  for (int i = n - 2; i >= 0; i--)
    p[i] = a[i].p * p[i + 1] + (1 - a[i].p) * (p[i + 1] + 1);
  double ans = 0;
  for (int i = 0; i < n; i++) ans += a[i].l * (1 + a[i].p * p[i + 1]);
  printf("%.8f\n", ans);
  return 0;
}
