#include <bits/stdc++.h>
using namespace std;
const int64_t N = 50005;
int64_t n;
struct node {
  int64_t l, p;
  bool operator<(const node& rhs) const {
    return l * p * (100 - rhs.p) > rhs.l * rhs.p * (100 - p);
  }
} data[N];
int main() {
  scanf("%lld", &n);
  double sum = 0.0;
  for (int64_t i = 1; i <= n; i++) {
    scanf("%lld%lld", &data[i].l, &data[i].p);
    sum += 1.0 - 0.01 * data[i].p;
  }
  sort(data + 1, data + n + 1);
  double ans = 0.0;
  for (int64_t i = 1; i <= n; i++) {
    sum -= (1.0 - data[i].p * 0.01);
    ans += (1.0 + sum * data[i].p * 0.01) * data[i].l;
  }
  printf("%.10lf\n", ans);
}
