#include <bits/stdc++.h>
using namespace std;
const int N = 5e4 + 10;
int n;
int l[N], p[N];
double ans, prelen;
int idx[N];
int cmp(int a, int b) {
  return p[a] * l[a] / (100.0 - p[a]) > p[b] * l[b] / (100.0 - p[b]);
}
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; ++i) {
    scanf("%d%d", l + i, p + i);
  }
  for (int i = 0; i < n; ++i) {
    idx[i] = i;
  }
  sort(idx, idx + n, cmp);
  for (int ii = 0; ii < n; ++ii) {
    int i = idx[ii];
    ans += (1 - p[i] / 100.0) * prelen + l[i];
    prelen += p[i] / 100.0 * l[i];
  }
  printf("%.10f\n", ans);
  return 0;
}
