#include <bits/stdc++.h>
using namespace std;
vector<pair<double, double> > data;
double p;
bool simulate(double t) {
  double totalPower = p;
  for (int i = 0; i < data.size(); i++) {
    double NeededPower = (data[i].first - data[i].second / t);
    if (NeededPower > 0) {
      totalPower -= NeededPower;
    }
    if (totalPower < 0) return false;
  }
  return true;
}
int main() {
  int n;
  cin >> n >> p;
  for (int i = 0; i < n; i++) {
    double a, b;
    cin >> a >> b;
    data.push_back(pair<double, double>(a, b));
  }
  double l = 0, r = 99999999999999;
  double mid;
  for (int i = 0; i < 100; i++) {
    mid = l + r;
    mid /= 2;
    if (simulate(mid)) {
      l = mid;
    } else {
      r = mid;
    }
  }
  if (simulate(l)) {
    mid = min(mid, l);
  }
  if (simulate(r)) {
    mid = min(mid, r);
  }
  if (mid == 99999999999999) {
    cout << -1 << endl;
  } else {
    printf("%.10lf\n", mid);
  }
  return 0;
}
