#include <bits/stdc++.h>
using namespace std;
template <class T>
void show(T *a, long long n) {
  for (int i = 0; i < n; ++i) cout << a[i] << ' ';
  cout << endl;
}
template <class T>
void show2(T *a, long long n, long long indexing = 0) {
  for (int i = 0; i < n; ++i) cout << i + indexing << ' ' << a[i] << '\n';
}
int indexOf(const string &s, const char c, long long l = -1) {
  if (l == -1) l = s.length();
  for (int i = 0; i < l; ++i)
    if (s[i] == c) return i;
  return -1;
}
class node {
 public:
  long long i, j, k;
  node() {
    i = 0;
    j = 0;
    k = 0;
  }
  node(long long a, long long b, long long c = 0) {
    i = a;
    j = b;
    k = c;
  }
  friend bool operator<(const node &c1, const node &c2);
  friend ostream &operator<<(ostream &o, const node &p);
};
bool operator<(const node &c1, const node &c2) {
  if (c1.i == c2.i) return c1.j < c2.j;
  return c1.i < c2.i;
}
ostream &operator<<(ostream &o, const node &p) {
  o << '(' << p.i << ' ' << p.j;
  if (p.k != 0) o << ' ' << p.k;
  o << ") ";
}
template <class T>
ostream &operator<<(ostream &o, const vector<T> v) {
  o << '[' << *v.begin();
  for (typename vector<T>::const_iterator it = v.begin() + 1; it != v.end();
       ++it)
    o << ' ' << *it;
  o << ']';
}
long long power(long long x, long long y = (1000000007 - 2),
                long long m = 1000000007) {
  if (y == 0) return 1;
  long long p = power(x, y / 2, m) % m;
  p = (p * p) % m;
  return (y % 2 == 0) ? p : (x * p) % m;
}
double Power(double x, long long y) {
  if (y == 0) return 1;
  double p = power(x, y / 2);
  p = (p * p);
  return (y % 2 == 0) ? p : (x * p);
}
long long fact[200005] = {1};
inline void factorial(long long l = 200005) {
  for (int i = 1; i < l; ++i) fact[i] = (fact[i - 1] * i) % 1000000007;
}
long long parray[200005] = {0};
void rprime(long long m, long long n) {
  for (int i = m % 2; i <= n - m; i += 2) parray[i] = 1;
  long long s = sqrt(n), x;
  for (int i = 3; i <= s; i += 2) {
    if (m > i)
      x = (m - 1) / i + 1;
    else {
      parray[i] = 1;
      x = 2;
    }
    while (i * x <= n) {
      parray[(i * x) - m] = 1;
      ++x;
    }
  }
  if (m == 1) parray[0] = 1;
  if (m == 0) {
    parray[0] = 1;
    parray[1] = 1;
  }
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  long long n = 0, m = 0, q = 0, t = 0, c = 0, d = 0, x = 0, y = 0, z = 0,
            i = 0, j = 0, k = 0, l = 0, r = 0, sum = 0, ans = 0, ans1 = 0,
            ans2 = 0, a[200005] = {0}, b[200005] = {0};
  string s, s1, s2, vos = "aeiou";
  char ch, ca[200005];
  cin >> n >> d;
  for (i = 0; i < n; ++i) cin >> a[i];
  double eff, maxe = -2.0;
  double e1, e2, e3;
  for (i = 0; i < n - 2; ++i) {
    e1 = double(a[i]);
    e2 = double(a[i + 1]);
    long long *i3 = lower_bound(a, a + n, a[i] + d);
    j = (i3 - a);
    if (j == n || a[j] > a[i] + d) --j;
    if (j > i + 1 && j < n) {
      e3 = double(a[j]);
      eff = (e3 - e2) / (e3 - e1);
      maxe = max(maxe, eff);
    }
  }
  if (maxe > -1)
    cout << fixed << setprecision(10) << maxe;
  else
    cout << -1;
}
