#include <bits/stdc++.h>
double eps = 1e-6;
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  int n;
  long long p, a[100010], b[100010];
  long long sum = 0;
  cin >> n >> p;
  for (int i = 0; i < n; ++i) {
    cin >> a[i] >> b[i];
    sum += a[i];
  }
  if (p >= sum) {
    cout << -1 << endl;
    return 0;
  }
  double lo = 0;
  double hi = 1e17;
  double mx = 0;
  for (int var = 0; var < 100; ++var) {
    mx = lo + (hi - lo) / 2;
    double need = 0;
    for (int i = 0; i < n; ++i) {
      need += max(mx * a[i] - b[i], 0 * 1.0);
    }
    if (p * mx >= need) {
      lo = mx + eps;
    } else {
      hi = mx - eps;
    }
  }
  printf("%.9f\n", lo);
  return 0;
}
