#include <bits/stdc++.h>
using namespace std;
const long long MOD1 = 1000000009;
const long long MOD2 = 1000000021;
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
long long lcm(long long a, long long b) {
  if (a == 0 || b == 0) return a + b;
  return a * (b / gcd(a, b));
}
int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};
int ddx[] = {0, 0, 1, 1, 1, -1, -1, -1}, ddy[] = {1, -1, 1, 0, -1, 1, 0, -1};
pair<double, double> p[50000];
int main() {
  int n;
  scanf("%d", &n);
  for (int(i) = (0); (i) <= (n - 1); (i) += (1)) {
    scanf("%lf%lf", &p[i].first, &p[i].second);
    p[i].second /= 100;
  }
  sort(p, p + n, [&](pair<double, double> p1, pair<double, double> p2) {
    return p1.first * p1.second * (1 - p2.second) >
           p2.first * p2.second * (1 - p1.second);
  });
  double ans = 0;
  double t = 0;
  for (int(i) = (0); (i) <= (n - 1); (i) += (1)) {
    ans += p[i].first + t * (1 - p[i].second);
    t += p[i].first * p[i].second;
  }
  printf("%.11f", ans);
}
