#include <bits/stdc++.h>
using namespace std;
bool dbg = 0;
clock_t start_time = clock();
void bad(string mes = "Impossible") {
  cout << mes;
  exit(0);
}
void bad(int mes) {
  cout << mes;
  exit(0);
}
template <typename T>
string bin(T x, int st = 2) {
  string ans = "";
  while (x > 0) {
    ans += char('0' + x % st);
    x /= st;
  }
  reverse(ans.begin(), ans.end());
  return ans.empty() ? "0" : ans;
}
template <typename T>
void amax(T& x, T y) {
  x = max(x, y);
}
template <typename T>
void amin(T& x, T y) {
  x = min(x, y);
}
inline int popcount(int x) {
  int count = 0;
  __asm__ volatile("POPCNT %1, %0;" : "=r"(count) : "r"(x) :);
  return count;
}
template <typename T>
T input() {
  T ans = 0, m = 1;
  char c = ' ';
  while (!((c >= '0' && c <= '9') || c == '-')) {
    c = getchar();
  }
  if (c == '-') m = -1, c = getchar();
  while (c >= '0' && c <= '9') {
    ans = ans * 10 + (c - '0'), c = getchar();
  }
  return ans * m;
}
template <typename T>
void read(T& a) {
  a = input<T>();
}
template <typename T>
void read(T& a, T& b) {
  read(a), read(b);
}
template <typename T>
void read(T& a, T& b, T& c) {
  read(a, b), read(c);
}
template <typename T>
void read(T& a, T& b, T& c, T& d) {
  read(a, b), read(c, d);
}
const int inf = 1e9 + 20;
const short short_inf = 3e4 + 20;
const long double eps = 1e-12;
const int maxn = (int)1e5 + 12, base = 1e9 + 7;
const long long llinf = 2e18 + 5;
template <typename T>
T binpow(T n, T second) {
  if (second <= 0) return 1LL;
  if (second % 2 == 0) {
    T b = binpow(n, second / 2);
    return (1LL * b * b) % base;
  } else {
    return (1LL * binpow(n, second - 1) * n) % base;
  }
}
int a[maxn], b[maxn];
int p;
bool can(const long double& tm, int n) {
  long double sumNeed = 0;
  for (int i = 0; i < n; i++) {
    long double cur = b[i];
    cur -= (long double)tm * a[i];
    if (cur <= 0) {
      sumNeed += (-cur) / (long double)p;
    }
  }
  if (sumNeed <= tm) return 1;
  return 0;
}
int main() {
  int n;
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n >> p;
  long long sumA = 0;
  for (int i = 0; i < n; i++) {
    cin >> a[i] >> b[i];
    sumA += a[i];
  }
  if (sumA <= p) {
    cout << -1;
    return 0;
  }
  long double l = 0, r = (long double)5e10;
  for (int it = 0; it < 500; it++) {
    long double m = (l + r) / (long double)2;
    if (can(m, n)) {
      l = m;
    } else {
      r = m;
    }
  }
  cout << fixed << setprecision(20) << l << '\n';
  return 0;
}
