#include <bits/stdc++.h>
using namespace std;
int n;
int p[50047], t[50047];
int A[50047];
bool smaller(int i, int j) {
  return t[i] * p[i] * (100 - p[j]) > t[j] * p[j] * (100 - p[i]);
}
int main() {
  scanf("%d", &n);
  for (int i = 0; i < (n); ++i) {
    scanf("%d%d", t + i, p + i);
    A[i] = i;
  }
  sort(A, A + n, smaller);
  long double buff = 0;
  long double total = 0;
  for (int i = 0; i < (n); ++i) {
    int x = A[i];
    total += t[x];
    total += buff * 0.01 * (100 - p[x]);
    buff += 0.01 * (p[x]) * t[x];
  }
  printf("%.15lf\n", (double)total);
}
