#include <bits/stdc++.h>
const int MAXN = 5e4 + 5;
std::pair<int, int> T[MAXN];
bool Cmp(const std::pair<int, int>& p1, const std::pair<int, int>& p2) {
  return p1.first * p1.second * (100 - p2.second) >
         p2.first * p2.second * (100 - p1.second);
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d%d", &T[i].first, &T[i].second);
  std::sort(T, T + n, Cmp);
  long double res = 0, listened = 0;
  for (int i = 0; i < n; i++) {
    res += T[i].first + listened * ((100.0 - T[i].second) / 100.0);
    listened += (T[i].second / 100.0) * T[i].first;
  }
  printf("%.10lf\n", (double)res);
}
