#include <bits/stdc++.h>
using namespace std;
const int NMAX = 50505;
struct song {
  int length, prob;
  bool operator<(const song& other) const {
    return (100 - other.prob) * prob * length >
           (100 - prob) * other.prob * other.length;
  }
};
int n, S[NMAX];
song L[NMAX];
void read() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d%d", &L[i].length, &L[i].prob);
  }
}
void solve() {
  double result = 0.0;
  for (int i = n; i >= 1; i--) {
    S[i] = S[i + 1] + (100 - L[i].prob);
    double probSucceed = (1.0 * L[i].prob / 100);
    double expectedAfter = (1.0 * S[i + 1] / 100);
    result += probSucceed * expectedAfter * L[i].length + L[i].length;
  }
  printf("%.10lf\n", result);
}
int main() {
  read();
  sort(L + 1, L + n + 1);
  solve();
  return 0;
}
