PARSER_BEGIN(Q1)

class Q1 {


  /** Standard code to call the parser
   */
  public static void main(String args[]) {

    Q1 parser;

    System.out.println("Reading from standard input . . .");
    parser = new Q1(System.in);
    try {
      parser.line();
      System.out.println("Yes");
     } catch (TokenMgrError e) {   // Lexical error
      System.out.println("No");
     } catch (ParseException e) {  // Parsing error
      System.out.println("No");
     }
  }   /* End of function "main" */


}

PARSER_END(Q1)



/******************/
/***** TOKENS *****/
/******************/

SKIP : /* WHITE SPACE */
{
  " " 
| "\t"
| "\n"
| "\r"
}

TOKEN :
{
  < LBR : "(" >
| < RBR : ")" >
| < X : "x" >
| <COMMA : "," >
}


/*************************/
/***** GRAMMAR RULES *****/
/*************************/

void line () : {}
{
  s() <EOF> 
}

void s () : {}
{
  <LBR> l() <RBR> 
| <X>
}

void l() : {}
{
  s() ( <COMMA> s() )*
}