#include <bits/stdc++.h>
using namespace std;
template <typename T1, typename T2>
inline void chkmin(T1 &x, T2 y) {
  if (x > y) x = y;
}
template <typename T1, typename T2>
inline void chkmax(T1 &x, T2 y) {
  if (x < y) x = y;
}
inline int readChar();
template <class T = int>
inline T readInt();
template <class T>
inline void writeInt(T x, char end = 0);
inline void writeChar(int x);
inline void writeWord(const char *s);
static const int buf_size = 4096;
inline int getChar() {
  static char buf[buf_size];
  static int len = 0, pos = 0;
  if (pos == len) {
    pos = 0, len = fread(buf, 1, buf_size, stdin);
  }
  if (pos == len) {
    return -1;
  }
  return buf[pos++];
}
inline int readChar() {
  int c = getChar();
  while (c <= 32) {
    c = getChar();
  }
  return c;
}
template <class T>
inline T readInt() {
  int s = 1, c = readChar();
  T x = 0;
  if (c == '-') s = -1, c = getChar();
  while ('0' <= c && c <= '9') x = x * 10 + c - '0', c = getChar();
  return s == 1 ? x : -x;
}
static int write_pos = 0;
static char write_buf[buf_size];
inline void writeChar(int x) {
  if (write_pos == buf_size)
    fwrite(write_buf, 1, buf_size, stdout), write_pos = 0;
  write_buf[write_pos++] = x;
}
template <class T>
inline void writeInt(T x, char end) {
  if (x < 0) writeChar('-'), x = -x;
  char s[24];
  int n = 0;
  while (x || !n) s[n++] = '0' + x % 10, x /= 10;
  while (n--) writeChar(s[n]);
  if (end) writeChar(end);
}
inline void writeWord(const char *s) {
  while (*s) writeChar(*s++);
}
struct Flusher {
  ~Flusher() {
    if (write_pos) fwrite(write_buf, 1, write_pos, stdout), write_pos = 0;
  }
} flusher;
using namespace std;
const int MAXN = 100001;
int n, p;
int a[MAXN], b[MAXN];
bool get(long double mid) {
  long double sum = 0;
  for (int i = 0; i < n; i++) {
    long double cnt = mid * a[i];
    long double need = cnt - b[i];
    if (need < 1e-15) {
      continue;
    }
    sum += need;
  }
  return sum <= mid * p;
}
int main() {
  n = readInt(), p = readInt();
  long long sum = 0;
  for (int i = 0; i < n; i++) {
    a[i] = readInt(), b[i] = readInt();
    sum += a[i];
  }
  if (sum <= p) {
    writeInt(-1, '\n');
    return 0;
  }
  long double l = 0.0;
  long double r = 1e18;
  for (int i = 0; i < 100; i++) {
    long double mid = (l + r) / 2.0;
    if (get(mid)) {
      l = mid;
    } else {
      r = mid;
    }
  }
  printf("%.9lf\n", (double)l);
  return 0;
}
