#include <bits/stdc++.h>
using namespace std;
struct eugin {
  double a, p;
};
int n;
eugin v[50010];
double ans;
bool operator<(eugin q, eugin w) {
  double t1, t2;
  t1 = q.a * q.p * (1 - w.p);
  t2 = w.a * w.p * (1 - q.p);
  if (t1 > t2) return true;
  return false;
}
int main() {
  int i;
  double pre;
  scanf("%d", &n);
  for (i = 1; i <= n; i++) {
    scanf("%lf%lf", &v[i].a, &v[i].p);
    v[i].p = v[i].p / 100.0;
  }
  sort(v + 1, v + 1 + n);
  pre = 0.0;
  ans = 0.0;
  for (i = 1; i <= n; i++) {
    ans += v[i].a + pre * (1 - v[i].p);
    pre += v[i].a * v[i].p;
  }
  printf("%.9lf\n", ans);
  return 0;
}
