#include <bits/stdc++.h>
using namespace std;
namespace {
namespace aimi {
template <class T>
void _input(T &x) {
  cin >> x;
}
void _input(int &x) { scanf("%d", &x); }
void _input(int64_t &x) { scanf("%" SCNd64, &x); }
void _input(double &x) { scanf("%lf", &x); }
void _input(char &x) { scanf(" %c", &x); }
void _input(char *x) { scanf("%s", x); }
void input() {}
void input(char *x) { scanf("%s", x); }
template <class T, class... U>
void input(T &head, U &...tail) {
  _input(head);
  input(tail...);
}
template <class T>
void _print(const T &x) {
  cout << x;
}
void _print(const int &x) { printf("%d", x); }
void _print(const int64_t &x) { printf("%" PRId64, x); }
void _print(const double &x) { printf("%.16f", x); }
void _print(const char &x) { putchar(x); }
void _print(const char *x) { printf("%s", x); }
template <class T>
void _print(const vector<T> &x) {
  for (auto i = cbegin(x); i != cend(x); _print(*i++))
    if (i != cbegin(x)) putchar(' ');
}
void print() {}
template <class T, class... U>
void print(const T &head, const U &...tail) {
  _print(head);
  putchar(sizeof...(tail) ? ' ' : '\n');
  print(tail...);
}
template <class T, class F = less<T>>
void sort_unique(vector<T> &v, F f = F()) {
  sort(begin(v), end(v), f);
  v.resize(unique(begin(v), end(v)) - begin(v));
}
template <class T>
inline T get_bit(T x, int i) {
  return (x >> i) & 1;
}
template <class T>
inline bool chkmax(T &a, const T &b) {
  return b > a ? a = b, true : false;
}
template <class T>
inline bool chkmin(T &a, const T &b) {
  return b < a ? a = b, true : false;
}
template <class T>
using MaxHeap = priority_queue<T>;
template <class T>
using MinHeap = priority_queue<T, vector<T>, greater<T>>;
const int MAX = 100005;
int n, u;
int a[MAX];
void main() {
  input(n, u);
  for (int i = 0; i < int(n); ++i) input(a[i]);
  double ans = -1e+100;
  for (int i = 0; i < int(n); ++i) {
    int k = int(prev(lower_bound(a + i, a + n, a[i] + u + 1)) - a);
    if (k - i < 2) continue;
    chkmax(ans, double(a[k] - a[i + 1]) / double(a[k] - a[i]));
  }
  if (ans < 0)
    print("-1");
  else
    print(ans);
}
}  // namespace aimi
}  // namespace
int main() {
  aimi::main();
  return 0;
}
