import java.util.Scanner;

public class usernames {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		int runs = scan.nextInt();
		scan.nextLine();
		
		for (int i=0; i<runs; i++) {
			int num = scan.nextInt()-2;
			System.out.print(scan.next());
			System.out.print(scan.next().substring(0, 2) + "_");
			
			for (int j=0; j<num; j++) {
				System.out.print(scan.next().substring(0,1));
			}
			System.out.println();
		}
	}

}