#include <bits/stdc++.h>
using namespace std;
struct ss {
  int l;
  double p, k;
} s[50005];
int func(ss a, ss b) { return a.k > b.k; }
int main() {
  int n;
  double d = 0, ans = 0;
  cin >> n;
  for (int i = 0; i < n; i++)
    cin >> s[i].l >> s[i].p, s[i].p /= 100,
        s[i].k = s[i].l * s[i].p / (1 - s[i].p);
  sort(s, s + n, func);
  for (int i = 0; i < n; i++)
    ans += s[i].l + d * (1 - s[i].p), d += s[i].l * s[i].p;
  cout << setprecision(15) << ans;
}
