#include <bits/stdc++.h>
using namespace std;
const int inf = 1999999999;
const double pi = acos(-1.0);
const double eps = 1e-9;
char gc() {
  char c;
  while (isspace(c = getchar()))
    ;
  return c;
}
int gs(char* s) {
  gets(s);
  int l = strlen(s);
  while (l && isspace(s[l - 1])) s[--l] = 0;
  return l;
}
int main() {
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  vector<pair<int, int> > v;
  for (int i = 0; i < n; i++) {
    int a, b;
    cin >> a >> b;
    v.push_back(make_pair(a, b));
  }
  long double low = 0, high = 1e10L, mid;
  for (int i = 0; i < 100; i++) {
    mid = (low + high) / 2;
    long double prev = -1e25L, t;
    bool ok = true;
    for (int j = 0; j < n; j++) {
      t = mid * v[j].second + v[j].first;
      if (v[j].second < 0 && t < prev) {
        ok = false;
        break;
      }
      if (v[j].second > 0) prev = max(prev, t);
    }
    if (!ok)
      high = mid;
    else
      low = mid;
  }
  if (high == 1e10L)
    cout << -1 << ('\n');
  else {
    cout.precision(20);
    cout << (low + high) / 2 << ('\n');
  }
  return 0;
}
