#include <bits/stdc++.h>
using namespace std;
const int inf = 1000000000;
const int N = 50009;
pair<int, int> a[N];
inline bool cmp(const pair<int, int> x, const pair<int, int> y) {
  return x.first * x.second * (100 - y.second) >
         y.first * y.second * (100 - x.second);
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d%d", &a[i].first, &a[i].second);
  sort(a, a + n, cmp);
  double f = 0.0;
  double acc = 0.0;
  for (int i = 0; i < n; i++) {
    int l = a[i].first, p = a[i].second;
    f += l + (1 - 1.0 * p / 100.0) * acc;
    acc += 1.0 * l * p / 100.0;
  }
  printf("%.9lf\n", f);
}
