import java.io.*;
import java.util.StringTokenizer;

public class boats
{
	
	static int N, M, P, Q;
	static int[][] streams;
	static boolean [][] whereisA, whereisB;

	public static void main(String[] args) throws IOException {
	
		BufferedReader in = new BufferedReader(new FileReader("boats.in"));
		PrintWriter out = new PrintWriter(new FileWriter("boats.out"));

		int n = Integer.parseInt(in.readLine());

		for (int i = 1; i <= n; i++) {

			StringTokenizer token = new StringTokenizer(in.readLine());		
	
			N = Integer.parseInt(token.nextToken());
			M = Integer.parseInt(token.nextToken());
			P = Integer.parseInt(token.nextToken());
			Q = Integer.parseInt(token.nextToken());		

			// fill in streams
			streams = new int[N][N];
			for (int j = 0; j < M; j++) {
				token = new StringTokenizer(in.readLine());
				int from = Integer.parseInt(token.nextToken());
				int to = Integer.parseInt(token.nextToken());
				int time = Integer.parseInt(token.nextToken());
				streams[from-1][to-1] = time;	
			}
	
			// what are the possible locations for A and B at each time step
			whereisA = new boolean[2000][N];
			whereisA[0][P-1] = true;
			fromHereA(P-1,0);
			whereisB = new boolean[2000][N];
			whereisB[0][Q-1] = true;
			fromHereB(Q-1,0);
			
			// could they ever meet?
			int time = 0;
			int meetingTime = -1;
			while (time < 2000 && meetingTime == -1) {
				
				for(int k=0; k<N; k++){
					if (whereisA[time][k] == true && whereisB[time][k] == true){
						meetingTime = time;
					}
				}
				time++;
			}
			
			if (meetingTime == -1) {
				out.println("Data Set " + i + ": Boats can never meet");
			}
			else {
				out.println("Data Set " + i + ": Boats can meet at time " + meetingTime);
			}

		} // end dataset for
		out.flush();
		out.close();

	} // end main



	public static void fromHereA(int rpoint, int time){
		for (int j=0; j<N; j++) {
			if (streams[rpoint][j] != 0) {
				int newtime = time + streams[rpoint][j];
				whereisA[newtime][j] = true;
				fromHereA(j,newtime);
			}
		}
	}
				

	public static void fromHereB(int rpoint, int time){
		for (int j=0; j<N; j++) {
			if (streams[rpoint][j] != 0) {
				int newtime = time + streams[rpoint][j];
				whereisB[newtime][j] = true;
				fromHereB(j,newtime);
			}
		}
	}	

}