#include <bits/stdc++.h>
using namespace std;
int N;
int L[50002], P[50002];
double A[50002], B[50002], S[50002];
int pos[50002];
inline bool compare(const int& i1, const int& i2) {
  if (A[i1] == 0 || A[i2] == 0) return A[i1] > A[i2];
  return B[i1] / A[i1] < B[i2] / A[i2];
}
int main() {
  cin.sync_with_stdio(false);
  cin >> N;
  double result = 0;
  for (int i = 1; i <= N; ++i) {
    cin >> L[i] >> P[i];
    result += L[i];
    A[i] = (1.0 * P[i] / 100) * L[i];
    B[i] = 1.0 * (100 - P[i]) / 100;
    pos[i] = i;
  }
  sort(pos + 1, pos + N + 1, compare);
  for (int i = 1; i <= N; ++i) S[i] = S[i - 1] + B[pos[i]];
  for (int i = 1; i <= N; ++i) result += A[pos[i]] * (S[N] - S[i]);
  cout << fixed << setprecision(9) << result << '\n';
}
