#include <bits/stdc++.h>
using namespace std;
;
const double eps = 1e-8;
const int mod = 1000000007;
const int maxn = 1e5 + 7;
const double pi = acos(-1);
const int inf = 0x3f3f3f3f;
const long long INF = 0x3f3f3f3f3f3f3f;
int n;
long long p;
struct node {
  long long a, b;
} num[maxn];
bool check(double x) {
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    if (x * num[i].a - num[i].b > eps) {
      ans += x * num[i].a - num[i].b;
    }
  }
  return x * p - ans > eps;
}
int main() {
  scanf("%d%lld", &n, &p);
  long long sum = 0;
  for (int i = 1; i <= n; i++) {
    scanf("%lld%lld", &num[i].a, &num[i].b);
    sum += num[i].a;
  }
  if (sum <= p) {
    printf("-1\n");
    return 0;
  }
  double ub = INF, lb = 0, mid;
  for (int i = 0; i <= 100; i++) {
    mid = (ub + lb) / 2;
    if (check(mid))
      lb = mid;
    else
      ub = mid;
  }
  printf("%.7f\n", ub);
  return 0;
}
