#include <bits/stdc++.h>
const int INF = (int)1e9;
const int mod = (int)1e9 + 7;
const int MAXN = (int)5e4 + 5;
using namespace std;
vector<pair<int, int>> st;
double expsum[MAXN];
bool cmp(pair<int, int> s1, pair<int, int> s2) {
  return s2.first * (s2.second / 100.0) * (1.0 - s1.second / 100.0) <
         s1.first * (s1.second / 100.0) * (1.0 - s2.second / 100.0);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    int a, b;
    cin >> a >> b;
    st.push_back(make_pair(a, b));
  }
  sort(st.begin(), st.end(), cmp);
  int i = 1;
  for (auto u : st) {
    int a = u.first;
    int b = u.second;
    expsum[i] = expsum[i - 1] + (double)a * b / 100.0;
    i++;
  }
  double ans = 0;
  i = 0;
  for (auto u : st) {
    int a = u.first;
    int b = u.second;
    ans = ans + a;
    ans = ans + expsum[i] * (100.0 - b) / 100.0;
    i++;
  }
  cout << fixed << setprecision(10) << ans << '\n';
}
