#include <bits/stdc++.h>
using namespace std;
class E {
 public:
  int l, p;
  E() {}
  E(int _l, int _p) {
    l = _l;
    p = _p;
  }
  bool operator<(const E &e) const {
    return l * (100 - e.p) * p > e.p * (100 - p) * e.l;
  }
} e[50005];
int main(void) {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d%d", &e[i].l, &e[i].p);
  sort(e, e + n);
  double ans = 0, val = 0;
  for (int i = n - 1; i >= 0; i--) {
    ans += e[i].p / 100.0 * e[i].l * val + e[i].l;
    val += (100.0 - e[i].p) / 100.0;
  }
  printf("%.9f\n", ans);
  return 0;
}
