#include <iostream>
#include <vector>
#define INF 1234567890
using namespace std;
int T, test_case, Answer, N, K;

int main() {
    cin >> T;
    for(test_case = 1; test_case <= T; test_case++) {
        Answer = 0;
        cin >> N;
        vector<int> a(N + 1);
        a[0] = 0; // 좌표 0
        for(int i = 1; i <= N; i++) cin >> a[i];
        a.push_back(INF);
        cin >> K;
        int start = 0;
        int tmp = 1;
        while(true) {
            if(start == N) break;
            int here = a[start];
            int next = a[tmp];
            if(next - here <= K) {
                if(a[tmp + 1] - here > K) {
                    Answer++;
                    start = tmp;
                }
                tmp++;
            } else {
                Answer = -1;
                break;
            }
        }
        cout << "Case #" << test_case << "\n";
        cout << Answer << "\n";
    }
    return 0;
}