#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const int INFL = 10000000000000000LL;
const double eps = 1e-9;
const double PI = acos(-1.0);
const int maxn = 5e4 + 10;
struct Node {
  int l, p;
  bool operator<(const Node& tmp) const {
    return (100 - tmp.p) * l * p > (100 - p) * tmp.l * tmp.p;
  }
} nds[maxn];
int n;
int main() {
  scanf("%d", &n);
  for (int i = 0; i < (n); i++) scanf("%d%d", &nds[i].l, &nds[i].p);
  sort(nds, nds + n);
  double sum = 0, ans = 0;
  for (int i = 0; i < (n); i++) {
    ans += nds[i].l;
    ans += (1 - nds[i].p * 1.0 / 100) * sum;
    sum += nds[i].l * (nds[i].p * 1.0 / 100);
  }
  printf("%.9lf\n", ans);
  return 0;
}
