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

public class tekst{
	public static void main(String argumendid[]){
		String tee=(".");
		File kataloog=new File(tee); 
		String failid[]=kataloog.list();
		String erisonad[]=new String[100];
		int a=0;
		int b=0;
		boolean poleolemas=true; 
		boolean esimene=true;	
	try{
	for (int i=0; i<failid.length; i++){ 
		BufferedReader sisse=new BufferedReader(new FileReader(failid[i]));  
		String rida=sisse.readLine(); 
		StringTokenizer st; 
		String sona;
		if (failid[i].endsWith(".txt")&&rida!=null){ 
		
			st=new StringTokenizer(rida, " ");
			if (esimene){
			sona=st.nextToken();
			erisonad[a]=sona;
			a++;
			esimene=false;
			}
			while(rida!=null){	 
				while(st.hasMoreTokens()){ 
					sona=st.nextToken();	
					poleolemas=true;				
						for(int w=0; w<a; w++){								
							if (sona.equals(erisonad[w])){
							poleolemas=false;
 							}
						}
						if (poleolemas){					
						erisonad[a]=sona;
						a++;	
						}
				}
				rida=sisse.readLine();
				if (rida!=null)st=new StringTokenizer(rida, " ");
				poleolemas=true; 
			}
			
		}
		sisse.close(); 
	}				
	} catch(Exception viga){System.out.println(viga);}
	
	System.out.println(a);
	for(int q=0; q<a; q++){
	System.out.println(erisonad[q]);

	}
	}
}