#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 50;
int n, p, first[N], second[N];
double tmin = 1e9;
pair<double, int> d[N];
bool ok(double x) {
  double tp = x * p;
  for (int i = 0; i < n; ++i) {
    tp -= max(first[i] * x - second[i], 0.0);
  }
  return tp >= 0;
}
int main() {
  cin.sync_with_stdio(0);
  cin >> n >> p;
  for (int i = 0; i < n; ++i) cin >> first[i] >> second[i];
  double lo = 0, hi = 1e20, mid;
  if (ok(hi)) {
    printf("-1");
  } else {
    for (int i = 0; i < 1000; ++i) {
      mid = (lo + hi) / 2;
      if (ok(mid))
        lo = mid;
      else
        hi = mid;
    }
    printf("%.6f", mid);
  }
  return 0;
}
