#include <bits/stdc++.h>
using namespace std;
pair<long long int, long long int> a[500001];
int main() {
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(10);
  long long int i, j, n, f;
  double lo, mid, hi, ans = -1, last;
  cin >> n;
  for (i = 1; i <= n; i++) cin >> a[i].first >> a[i].second;
  lo = 0;
  hi = 1e10;
  for (i = 0; i < 100; i++) {
    mid = (lo + hi) / 2.0;
    f = 0;
    last = -1e100;
    for (j = 1; j <= n; j++) {
      if (a[j].second > 0)
        last = max(last, 1.0 * (a[j].first + 1.0 * a[j].second * mid));
      else {
        if (1.0 * (a[j].first + 1.0 * a[j].second * mid) < last) {
          f = 1;
          break;
        }
      }
    }
    if (f) {
      hi = mid;
      ans = mid;
    } else
      lo = mid;
  }
  cout << ans;
  return 0;
}
