#include <bits/stdc++.h>
using namespace std;
const int MAXN = 50100;
int n, l[MAXN], p[MAXN], idx[MAXN];
double ev[MAXN], el[MAXN];
int idxCMP(int i, int j) {
  return p[i] * l[i] * (100 - p[j]) > p[j] * l[j] * (100 - p[i]);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> l[i] >> p[i];
    idx[i] = i;
  }
  sort(idx, idx + n, idxCMP);
  for (int i = 1; i <= n; i++) {
    ev[i] =
        ev[i - 1] + (el[i - 1] * (100 - p[idx[i - 1]]) / 100.0) + l[idx[i - 1]];
    el[i] = el[i - 1] + l[idx[i - 1]] * p[idx[i - 1]] / 100.0;
  }
  cout << fixed << setprecision(10) << ev[n] << endl;
}
