#include <bits/stdc++.h>
struct d {
  int len, p;
} data[50005];
int cmp(d a, d b) {
  return a.len * a.p * (100 - b.p) > b.len * b.p * (100 - a.p);
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d%d", &data[i].len, &data[i].p);
  std::sort(data, data + n, cmp);
  double ans = 0, zt = 0;
  for (int i = 0; i < n; i++) {
    ans += data[i].len + zt / 100.0 * (100 - data[i].p);
    zt += data[i].len / 100.0 * data[i].p;
  }
  printf("%.10lf", ans);
  return 0;
}
