#include <bits/stdc++.h>
using namespace std;
const long double Pi = 3.14159265359;
const long MOD = (long)1e9 + 7;
long long const MAXN = (long long)5e4 + 10;
pair<long long, long long> a[MAXN];
bool CMP(pair<long long, long long> a, pair<long long, long long> b) {
  return a.first * a.second * (100 - b.second) >
         b.first * b.second * (100 - a.second);
}
int main() {
  ios::sync_with_stdio(false);
  cout.precision(16);
  long double out = 0.0;
  long long n;
  cin >> n;
  for (int i = 0; i < n; i++) cin >> a[i].first >> a[i].second;
  sort(a, a + n, CMP);
  long long s = 0;
  for (int i = 0; i < n; i++) s += (100 - a[i].second);
  long double c, d;
  for (int i = 0; i < n; i++) {
    s -= (100 - a[i].second);
    c = 1.0 + (s / 1.0 / 100.0);
    out = out +
          a[i].first * ((c * a[i].second + (100 - a[i].second)) / 1.0 / 100.0);
  }
  cout << fixed << out;
  return 0;
}
