#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("-O3")
using ld = long double;
const long long int mod = 1000000007;
const long long int inf = 1000000000000000000;
const long long int rk = 256;
const ld PI = 3.141592653589793;
ostream& operator<<(ostream& os, pair<long long int, long long int> const& x) {
  os << x.first << "," << x.second;
  return os;
}
template <class T>
ostream& operator<<(ostream& os, vector<T> const& x) {
  os << "{ ";
  for (auto& y : x) os << y << " ";
  return os << "}";
}
template <class T>
ostream& operator<<(ostream& os, set<T> const& x) {
  os << "{ ";
  for (auto& y : x) os << y << " ";
  return os << "}";
}
template <class Ch, class Tr, class Container>
basic_ostream<Ch, Tr>& operator<<(basic_ostream<Ch, Tr>& os,
                                  Container const& x) {
  os << "{ ";
  for (auto& y : x) os << y << " ";
  return os << "}";
}
template <class X, class Y>
ostream& operator<<(ostream& os, pair<X, Y> const& p) {
  return os << "[ " << p.first << ", " << p.second << "]";
}
struct comp {
  bool operator()(int const& i, int const& j) const { return i > j; }
};
struct Triplet {
  long long int x, y, z;
};
long long int modularexpo(long long int x, long long int n, long long int mod) {
  long long int res = 1;
  while (n > 0) {
    if (n % 2 == 1) res = (res * x) % mod;
    x = (x * x) % mod;
    n = n / 2;
  }
  return res;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long int n, u;
  cin >> n >> u;
  long long int arr[n];
  for (long long int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  long double ans = -1;
  for (long long int i = 0; i < n - 2; i++) {
    long long int cur = arr[i];
    long long int nex = arr[i + 1];
    long long int lo = i + 2, hi = n - 1;
    while (lo < hi) {
      long long int mid = (lo + hi) / 2;
      if (cur + u >= arr[mid]) {
        long double cal = ((arr[mid] - nex) * 1.0) / ((arr[mid] - cur) * 1.0);
        ans = max(cal, ans);
        lo = mid;
      } else
        hi = mid;
      if (hi - lo == 1) break;
    }
    if (cur + u >= arr[hi]) {
      long double cal = ((arr[hi] - nex) * 1.0) / ((arr[hi] - cur) * 1.0);
      ans = max(cal, ans);
    }
    if (cur + u >= arr[lo]) {
      long double cal = ((arr[lo] - nex) * 1.0) / ((arr[lo] - cur) * 1.0);
      ans = max(cal, ans);
    }
  }
  cout << setprecision(25) << ans << '\n';
  return 0;
}
