#include <bits/stdc++.h>
const int MAX = 50001;
int N;
struct song {
  double l, p;
  bool operator<(const song &cmp) const {
    return l * p * (100 - cmp.p) > cmp.l * cmp.p * (100 - p);
  }
} S[MAX];
int main() {
  while (~scanf("%d", &N)) {
    for (int i = 0; i < N; ++i) scanf("%lf%lf", &S[i].l, &S[i].p);
    std::sort(S, S + N);
    double ans = 0.0, sum = 0.0;
    for (int i = 0; i < N; ++i) {
      ans += S[i].l;
      ans += sum * (100 - S[i].p) * 0.01;
      sum += S[i].l * S[i].p * 0.01;
    }
    printf("%lf\n", ans);
  }
}
