class TrieNode
{
    public TrieNode[] Child = new TrieNode[10];
    public bool WordEnd = false;
}

class Trie
{
    public TrieNode Root = new TrieNode();
    
    // Inserts s into the Trie and also checks if s is a prefix or has a prefix in the Trie.
    public bool Insert(string s)
    {
        bool hasPrefix = false;
        bool isPrefix = true;
        TrieNode currentNode = this.Root;
        
        foreach(char ch in s)
        {
            if (currentNode.WordEnd)
            {
                hasPrefix = true;
            }
            
            int index = ch - 'a';
            
            if (currentNode.Child[index] == null)
            {
                currentNode.Child[index] = new();
                isPrefix = false;
            }
            
            currentNode = currentNode.Child[index];
        }
        
        currentNode.WordEnd = true;
        
        return hasPrefix || isPrefix;
    }
}

class Result
{
    public static void noPrefix(List<string> words)
    {
        Trie trie = new();
        
        foreach (string word in words)
        {
            bool prefix = trie.Insert(word);
            
            if (prefix)
            {
                Console.WriteLine("BAD SET");
                Console.WriteLine(word);
                return;
            }
        }
        
        Console.WriteLine("GOOD SET");
    }
}