#include <bits/stdc++.h>
using namespace std;
struct song {
  int l, p;
} a[50005];
int n;
double ans, s;
bool cmp(song a, song b) {
  return a.l * a.p * (100 - b.p) > b.l * b.p * (100 - a.p);
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) scanf("%d%d", &a[i].l, &a[i].p);
  sort(a + 1, a + n + 1, cmp);
  for (int i = 1; i <= n; i++) {
    ans += a[i].l + s * (100 - a[i].p) / 100.0;
    s += a[i].l * a[i].p / 100.0;
  }
  printf("%.10lf\n", ans);
  return 0;
}
