public static String pedirDni(){
		boolean correcto=false;
		String dni="";
		try{
			do{
			System.out.print("DNI => ");
			BufferedReader stdin=new BufferedReader(new InputStreamReader(System.in));
			dni=stdin.readLine();
			correcto=Operaciones.isdni(dni);
			}while(correcto==false);
		}catch(Exception e){
			System.out.println("Error "+e);
		}
		return dni;
	}