#include <stdio.h>

#include <stdlib.h>

#define MAX(a,b) ((a)>(b)?(a):(b))

#define MIN(a,b) ((a)<(b)?(a):(b))

#define INF 1000000

#define filer() freopen("in.txt","r",stdin)

#define filew() freopen("out.txt","w",stdout)

typedef long long ll;

typedef unsigned long long llu;

int arr[100005], n, k, res[100005];

int cmp(const void *a, const void *b){ return *(int*)a - *(int*)b; }

int lBound(int *a, int len, int x){

int lo = 0, hi = len, mid;

while ( lo + 1 < hi ){

mid = ( lo + hi ) >> 1;

if ( a[mid] > x ) hi = mid;

else lo = mid;

}

return lo;

}

int main(){

int test, ks, i, nxt, flag;

while ( scanf("%d", &test) == 1 ){

for ( ks = 1 ; ks <= test ; ks++ ){

scanf("%d%d", &n, &k);

flag = 1;

for ( i = 0 ; i < n ; i++ ) scanf("%d", &arr[i]);

qsort(arr, n, sizeof(int), cmp);

res[n] = 0;

for ( i = n - 1 ; i >= 0 ; i-- ){

res[i] = 0;

nxt = lBound(arr, n, arr[i] + 2*k);

if ( nxt - i >= 2 ){

res[i] = 1 + res[nxt+1];

if ( nxt - 1 - i >= 2 ) res[i] = MIN((1 + res[nxt]), res[i]);

if ( nxt - 2 - i >= 2 ) res[i] = MIN((1 + res[nxt-1]), res[i]);

}

else res[i] = INF;

}

printf("Case %d: %d\n", ks, (res[0] < INF) ? res[0] : -1);

}

}

return 0;

}