#include <bits/stdc++.h>
using namespace std;
template <typename T>
T nextInt() {
  T x = 0, p = 1;
  char ch;
  do {
    ch = getchar();
  } while (ch <= ' ');
  if (ch == '-') {
    p = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = x * 10 + (ch - '0');
    ch = getchar();
  }
  return x * p;
}
const int maxN = (int)5e5 + 10;
const int INF = (int)1e9;
const int mod = (int)1e9 + 7;
const long long LLINF = (long long)1e18;
int n;
vector<pair<int, int> > a;
const long double inf = 2e9;
bool ok(long double x) {
  long double rightmost = -inf * inf;
  for (int i = 0; i < n; ++i) {
    long double xx = a[i].first + a[i].second * x;
    if (a[i].second > 0) {
      rightmost = max(rightmost, xx);
    } else {
      if (rightmost > xx) return true;
    }
  }
  return false;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n;
  a.resize(n);
  for (int i = 0; i < n; ++i) {
    cin >> a[i].first >> a[i].second;
  }
  sort(a.begin(), a.end());
  if (!ok(inf)) {
    cout << -1 << '\n';
    return 0;
  }
  long double lf = 0, rg = inf;
  for (int i = 0; i < 100; ++i) {
    long double mid = (lf + rg) / 2;
    if (ok(mid)) {
      rg = mid;
    } else {
      lf = mid;
    }
  }
  cout.precision(13);
  cout << (lf + rg) / 2.0;
  return 0;
}
