import java.util.Scanner;

public class Froggy {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int N = scan.nextInt() , R = scan.nextInt();

        int[] arr = new int[N];
        for(int i = 0 ; i < arr.length ; ++i)arr[i] = scan.nextInt();
        int l = 0 , r = 1 , ans = 0;
        while(r < N) {
            if(arr[r] - arr[l] > R) {
                System.out.println(arr[r]  + " " + arr[l]);
                ans = - 1;
                break;
            }
            while(r < N && arr[r] - arr[l] <= R) {
                r++;
            }
            ans++;
            l = r - 1;
            r = l + 1;
        }
        System.out.println(ans);
    }
}