#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  int n;
  long long p;
  cin >> n >> p;
  vector<pair<double, long long>> v(n);
  for (int i = 0; i < n; ++i) {
    cin >> v[i].second >> v[i].first;
    v[i].first /= v[i].second;
  }
  sort(v.begin(), v.end());
  double tp = 0;
  long long sum_a = 0;
  for (int i = 1; i < n; ++i) {
    sum_a += v[i - 1].second;
    if ((v[i].first - tp) * p >= sum_a * (v[i].first - v[i - 1].first)) {
      tp += sum_a * (v[i].first - v[i - 1].first) / p;
    } else {
      cout << setprecision(10)
           << v[i - 1].first + p * (v[i - 1].first - tp) / (sum_a - p) << endl;
      return 0;
    }
  }
  sum_a += v[n - 1].second;
  if (p >= sum_a) {
    cout << -1 << endl;
  } else {
    cout << setprecision(20)
         << v[n - 1].first + p * (v[n - 1].first - tp) / (sum_a - p);
  }
  return 0;
}
