#include <bits/stdc++.h>
using namespace std;

int main() {
  ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  int n,s,c; cin>>n;
  map<int,vector<int>> mp;
  for (int i=0; i<n; i++)
    cin>>s>>c, mp[s].push_back(c);
  double ret=0;
  for (auto &[k,v] : mp) {
    sort(v.begin(),v.end());
    int n=v.size();
    for (int i=0; 2*i<n; i++)
      ret+=log(v[n-1-i])-log(v[i]);
  }
  cout<<setprecision(15)<<fixed<<ret<<"\n";
  return 0;
}