#include <bits/stdc++.h>
using namespace std;
int nod1(int a, int b) { return a ? nod1(b % a, a) : b; }
int nod(int a, int b) {
  if (a > b) swap(a, b);
  return nod1(a, b);
}
int nok(int a, int b) { return a / nod(a, b) * b; }
long long sum(vector<int> v) {
  long long ans = 0;
  for (int i = 0; i < v.size(); i++) ans += v[i];
  return ans;
}
bool letter(char c) { return 'a' <= c && c <= 'z'; }
bool LETTER(char c) { return 'A' <= c && c <= 'Z'; }
string intToStr1(long long n) {
  return n ? intToStr1(n / 10) + (char)('0' + n % 10) : "";
}
string intToStr(long long n) { return n ? intToStr(n) : "0"; }
long long strToInt(string s) {
  long long ans = 0;
  for (int i = 0; i < s.size(); i++) ans = 10 * ans + (s[i] - '0');
  return ans;
}
bool digit(char c) { return '0' <= c && c <= '9'; }
bool prime(int n) {
  if (n == 1) return 0;
  for (int i = 2; i * i <= n; i++)
    if (n % i == 0) return 0;
  return 1;
}
const double zero = 0;
const long long null = 0;
const long long INF = 1e18;
const long long MOD = 1000000007;
const double PI = atan2(0, -1);
const int MAXN = 200001;
const double eps = 1e-8;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, 1, 0, -1};
vector<long long> a, b;
vector<pair<double, int>> q;
int main() {
  cout.precision(200);
  cin.sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long n, p;
  cin >> n >> p;
  a.resize(n);
  b.resize(n);
  long long suma = 0, sumb = 0;
  for (int i = 0; i < n; i++) cin >> a[i] >> b[i], suma += a[i], sumb += b[i];
  if (suma <= p) {
    cout << -1;
    return 0;
  }
  double l = 0, r = 1e18;
  for (int i = 0; i < 200; i++) {
    double med = (r + l) / (double)(2);
    double sum = 0;
    for (int j = 0; j < n; j++)
      sum += max((double)(0), (a[j] * med - b[j]) / med);
    if (sum <= p)
      l = med;
    else
      r = med;
  }
  cout << l;
  return 0;
}
