options {
  LOOKAHEAD=1;
}


PARSER_BEGIN(Q2)

public class Q2 {
    /*** Main routine - call parser, print answer ***/
    public static void main(String args[]) throws ParseException {
        int decimal_val = 0;
	Q2 parser = new Q2(System.in);
	try {
	  decimal_val = parser.bcd_num();
          System.out.println("Decimal Equivalent:" + decimal_val);
	} catch (ParseException x) {
	  System.out.println("Exiting due to parse error.");
	  throw x;
	}
    }

}

PARSER_END(Q2)


SKIP : /*** Ignoring spaces/tabs ***/
{
    " "
  | "\t"
}



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


int bcd_num() :
{
  int digit_val=0;
  int scale=1;  // Power of 10 to raise number to...
  int ans=0;
}
{
  ( digit_val=bcd_digit() 
    { ans = ans + (digit_val * scale);
      scale = scale * 10;
    } 
  )+ (<EOF> | "\n" | "\r")
    {
      return ans;
    }
}



int bcd_digit() :
{
  int n1, n2, n3, n4;
}
{ // Four binary numbers -
  n1=numeral() n2=numeral() n3=numeral() n4=numeral()
  {
    int val = (n1*8) + (n2*4) + (n3*2) + (n4);
    if (val > 9) {  // A little semantic checking...
      System.err.println("BCD number too large: " +n1+n2+n3+n4+ " is " + val);
      throw new ParseException();
    }
    else
      return val;
  }
}

int numeral() :
{}
{
  "0" { return 0; }
| "1" { return 1; }
}