#include <bits/stdc++.h>
using namespace std;
struct node {
  int t;
  double p;
} d[50005];
bool operator<(const node &a, const node &b) {
  return a.t * a.p * (1 - b.p) > b.t * b.p * (1 - a.p);
}
int n;
double ans = 0, len = 0;
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    scanf("%d %lf", &d[i].t, &d[i].p);
    d[i].p /= 100.0;
  }
  sort(d, d + n);
  for (int i = 0; i < n; i++) {
    ans += d[i].t;
    ans += len * (1.0 - d[i].p);
    len += d[i].t * d[i].p;
  }
  printf("%lf\n", ans);
}
