#include <bits/stdc++.h>
int n;
struct node {
  int l;
  double p;
  node(int ll, double pp) : l(ll), p(pp) {}
  node() {}
} A[50004];
bool cmp(node a, node b) {
  return a.p * a.l / (1 - a.p) < b.p * b.l / (1 - b.p);
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    int l, p;
    scanf("%d%d", &l, &p);
    A[i] = node(l, p / 100.0);
  }
  double ans = 0;
  std::sort(A + 1, A + 1 + n, cmp);
  double cnt = 0;
  for (int i = 1; i <= n; i++) {
    ans = ans + A[i].p * (1 + cnt) * A[i].l;
    ans = ans + (1 - A[i].p) * A[i].l;
    cnt += (1 - A[i].p);
  }
  printf("%.12f\n", ans);
  return 0;
}
