#include <bits/stdc++.h>
using namespace std;
void _fill_int(int* p, int val, int rep) {
  int i;
  for (i = 0; i < rep; i++) p[i] = val;
}
int GETi() {
  int i;
  scanf("%d", &i);
  return i;
}
template <class T>
T sqr(T val) {
  return val * val;
}
int N;
signed long long L[50001], P[50001];
vector<int> V;
bool comp(const int& a, const int& b) {
  signed long long as = L[a] * P[a] * (100 - P[b]);
  signed long long bs = L[b] * P[b] * (100 - P[a]);
  return as > bs;
}
void solve() {
  int f, r, i, j, k, l;
  double ss;
  int x, y;
  N = GETi();
  for (i = 0; i < N; i++) {
    L[i] = GETi();
    P[i] = GETi();
    V.push_back(i);
  }
  sort(V.begin(), V.end(), comp);
  double TT = 0, S = 0;
  for (i = 0; i < N; i++) {
    S += L[V[i]] + TT * (100 - P[V[i]]) / 100.0;
    TT += L[V[i]] * P[V[i]] / 100.0;
  }
  printf("%.13lf\n", S);
  return;
}
int main(int argc, char** argv) {
  if (argc > 1) freopen(argv[1], "r", stdin);
  solve();
  return 0;
}
