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.prog();
      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 :
{
  < IF : "if" >
| < THEN : "then" >
| < ELSE : "else" >
| < FI : "fi" >
| < WHILE : "while" >
| < DO : "do" >
| < OD : "od" >
| < ID : "id" >
| < NUM : "num" >
| < ASSIGN : ":=" >
| < COMMA : "," >
}


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

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

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

void e() : {}
{
  <IF> e() <THEN> e() <ELSE> e() <FI>
| <WHILE> e() <DO> e() <OD>
| <ID> [ <ASSIGN> <NUM> ]  
}