package week05.laboratory;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.StringTokenizer;
public class joi2019_ho_t4 {
public static void main(String[] args) throws IOException {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(System.out));
int t = Integer.parseInt(reader.readLine());
for (int i = 0; i < t; i++) {
HashMap<String, List<String>> directedGraph = new HashMap<>();
HashMap<String, Boolean> visitedNodes = new HashMap<>();
int m = Integer.parseInt(reader.readLine());
for (int j = 0; j < m; j++) {
StringTokenizer tokenizer = new StringTokenizer(reader.readLine());
String from = tokenizer.nextToken();
String to = tokenizer.nextToken();
directedGraph.putIfAbsent(from, new ArrayList<>());
directedGraph.putIfAbsent(to, new ArrayList<>());
directedGraph.get(from).add(to);
}
boolean hasCycle = false;
for (String drink : directedGraph.keySet()) {
hasCycle = dfs(drink, directedGraph, visitedNodes);
if (hasCycle) break;
}
writer.write("Case " + (i + 1) + ": ");
if (hasCycle) {
writer.write("No");
} else {
writer.write("Yes");
}
writer.newLine();
writer.flush();
}
writer.close();
}
private static boolean dfs(
String node,
HashMap<String, List<String>> directedGraph,
HashMap<String, Boolean> visitedNodes) {
visitedNodes.put(node, true);
for (String nextDrink : directedGraph.get(node)) {
if (!visitedNodes.containsKey(nextDrink)) {
if (dfs(nextDrink, directedGraph, visitedNodes)) {
return true;
}
} else if (visitedNodes.get(nextDrink)) {
return true;
}
}
visitedNodes.put(node, false);
return false;
}
}
