C

#include <bits/stdc++.h>
#define ll long long
#define sc 1000000

using namespace std;

ll N, U ;

ll arr[100009] ;
float dp[100009] ;
bool mark = true ;

float solve(ll idx, ll i, ll j, ll k)
{
    if(idx == N)
        return 0 ;

    if(i != -1 && j != -1 && k != -1)
    {
        if(arr[k] - arr[i] > U)
        {
            return 0;
        }

        double p ;
        p = ((double)((1.0)*(arr[k]-arr[j])/(arr[k]-arr[i]))) * 1.0 ;


        return  p ;
    }

    float ret = 0 ;

    if(i == -1)
    {
        ret = max(solve(idx+1, idx, j, k), solve(idx+1, i, j, k)) ;
    }
    else if(j == -1)
    {
        ret = max(solve(idx+1, i, idx, k), solve(idx+1, i, j, k)) ;

    }
    else if(k == -1)
    {
        ret = max(solve(idx+1, i, j, idx), solve(idx+1, i, j, k)) ;

    }

    return dp[idx] = ret  ;

}

int main()
{
    cin >> N >> U ;


    for(ll i = 0 ; i < N  ; i++)
    {
        cin >> arr[i] ;
    }


    for(ll i = 0 ; i < 100001 ; i++)
    {
        dp[i] = -1 ;
    }


    float s ;

    s = solve(0, -1,-1,-1) ;

    if(s == 0)
        cout << -1 << endl ;
    else
        cout << s << endl  ;


    return 0;
}