#include <bits/stdc++.h>
const int Maxn = 50005;
int N, A[Maxn];
double L[Maxn], P[Maxn], Sum[Maxn], Ans;
using namespace std;
bool Cmp(const int &i, const int &j) {
  return (L[i] * P[i] * (1 - P[j] / 100)) > (L[j] * P[j] * (1 - P[i] / 100));
}
int main() {
  scanf("%d", &N);
  for (int i = 1; i <= N; ++i) {
    scanf("%lf%lf", &L[i], &P[i]);
    A[i] = i;
  }
  sort(A + 1, A + 1 + N, Cmp);
  for (int i = 1; i <= N; ++i) Sum[i] = Sum[i - 1] + L[A[i]] * P[A[i]];
  for (int i = 1; i <= N; ++i) Ans += L[i] * 10000;
  for (int i = 2; i <= N; ++i) Ans += (100 - P[A[i]]) * Sum[i - 1];
  cout << setprecision(12) << setiosflags(ios ::fixed) << Ans / 10000 << endl;
  return 0;
}
