/**
 * Created by Zhenyi Luo on 15-5-23.
 */
import java.util.Scanner;

public class Main {
    private static void solve(Scanner sc) {
        sc.nextLine();
        String s = sc.nextLine();
        int K = sc.nextInt();
        int len = s.length();
        int n = 1;
        for(; n*K < len; n++){
        }

        int missed = n*K - len;
        int numLastLine = K - missed;
        StringBuilder[] sbs = new StringBuilder[n];
        for(int i = 0; i < n; i++){
            sbs[i] = new StringBuilder();
        }
        int index = 0;
        for(int j = 0; j < K; j++){
            for(int i = 0; i < n; i++){
                if(i!= n-1){
                    sbs[i].append(s.charAt(index++));
                }else{
                    if(j < numLastLine){
                        sbs[i].append(s.charAt(index++));
                    }
                }
            }
        }
        StringBuilder sb = new StringBuilder();
        for(int i = 0; i < n; i++){
            sb.append(sbs[i]);
        }
        System.out.println(sb.toString());
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int T = sc.nextInt();
        for(int i = 0; i < T; i++){
            System.out.println("Case #" + (i+1) + ":");
            solve(sc);
        }
        sc.close();
    }
}