#include <bits/stdc++.h>
using namespace std;
struct song {
  double l, p;
  bool operator<(const song &x) const {
    return l * p * (1 - x.p) < x.l * x.p * (1 - p);
  }
} s[50005];
int n;
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    int l, p;
    scanf("%d %d", &l, &p);
    s[i].l = (double)l, s[i].p = (double)p / 100.0;
  }
  sort(s, s + n);
  double ans = 0.0, cump = 0.0;
  for (int i = 0; i < n; i++) {
    ans += s[i].l * (1 + s[i].p * cump);
    cump += 1 - s[i].p;
  }
  printf("%.9f\n", ans);
  return 0;
}
