#include <bits/stdc++.h>
using namespace std;
long long mod = 1e9 + 7;
long double eps = 1e-12;
long long dx[] = {0, 0, 1, -1};
long long dy[] = {1, -1, 0, 0};
long long n, res = 0, k = 0, h, ans = 0, m, level = 0;
;
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long lcm(long long x, long long y) { return (x * y) / gcd(x, y); }
void yes() { cout << "Yes\n"; }
void no() { cout << "No\n"; }
vector<long long> v[300005], vnode;
void add_edge(long long x, long long y) {
  v[x].push_back(y);
  v[y].push_back(x);
}
string s2, ch = "", s = "", s1 = "", t;
vector<pair<string, long long> > vm;
vector<pair<pair<long long, long long>, long long> > vvvl, vvvr;
vector<pair<long long, long long> > vv, vv2;
long long a[500005], b[500005];
map<long long, long long> mp;
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  long long i = 0, x = 0, z = 0, y = 0, j = 0, q, mx = 0, mm, idx = 0, ok = 0,
            l = 0, r, negatif = 0, positif = 0, l1, r1, p;
  set<long long>::iterator it, it2;
  multiset<long long>::iterator it1;
  multiset<long long> mst1, mst2;
  cin >> n >> m;
  for (i = 1; i <= (long long)(n); i++) cin >> a[i];
  long double res = -1.00;
  for (i = 1; i <= (long long)(n - 2); i++) {
    x = a[i] + m;
    idx = upper_bound(a + i + 2, a + 1 + n, x) - a - 1;
    if (idx <= (i + 1)) continue;
    long double ans = 1 + (a[i] - a[i + 1]) / (long double)(a[idx] - a[i]);
    if ((ans - res) >= eps) res = ans;
  }
  for (i = n; i >= 3; i--) {
    x = a[i] - m;
    idx = lower_bound(a + 1, a + i + 1, x) - a;
    if (idx >= (i - 1)) continue;
    long double ans = 1 + (a[idx] - a[idx + 1]) / (long double)(a[i] - a[idx]);
    if ((ans - res) >= eps) res = ans;
  }
  cout << setprecision(10) << res;
  return 0;
}
