#include <array>
#include <cassert>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <utility>
#include <vector>

using namespace std;

struct arraycomp {
  bool operator()(const array<int64_t, 3>& a, const array<int64_t, 3>& b) const {
    return a[0] * b[1] < a[1] * b[0];
  }
};

int main() {
  int n;
  cin >> n;
  vector<array<int64_t, 2>> v(n);
  int64_t contrib = 0;
  for(auto& x: v) {
    cin >> x[0] >> x[1];
    contrib += x[0] * x[1];
  }
  if(contrib == 0) return void(cout << "0\n"), 0;
  if(contrib > 0) {
    for(auto& x: v) x[0] *= -1;
    contrib *= -1;
  }
  assert(contrib < 0);
  double ret = 0;
  priority_queue<array<int64_t, 3>, vector<array<int64_t, 3>>, arraycomp> q;
  map<int64_t, array<int64_t, 2>> dp;
  for(int i = 0; i < n; i++) {
    auto [loc, weight] = v[i];
    dp[loc] = {weight, 1};
    q.push(array<int64_t, 3>({weight, 1, loc}));
  }
  while(true) {
    assert(q.size());
    auto [totweight, totnum, loc] = q.top(); q.pop();
    if(dp[loc] != array<int64_t, 2>({totweight, totnum})) continue;
    if(dp.upper_bound(loc) == dp.end()) {
      ret += (-contrib) / double(dp[loc][0]) * dp[loc][1];
      break;
    }
    dp.erase(loc);
    auto it = dp.upper_bound(loc); assert(it != dp.end());
    int64_t maxshift = (it->first - loc) * totweight;
    if(maxshift + contrib >= 0) {
      ret += (-contrib) / double(totweight) * totnum;
      break;
    }
    contrib += maxshift;
    auto nxtloc = it->first;
    ret += (nxtloc - loc) * totnum;
    auto [nweight, nnum] = dp[nxtloc];
    dp[nxtloc] = {nweight + totweight, nnum + totnum};
    q.push({(nweight + totweight), (nnum + totnum), nxtloc});
  }
  cout << fixed << setprecision(39) << ret << "\n";
}