%{
  #include <stdlib.h> /* Required to compile with C++ */
  #include <stdio.h>
  #include <ctype.h>
  extern int yyparse(); /* Required to compile with C++ */
  extern void yyerror(char*); /* Required to compile with C++ */
  extern int yylex(void); /* Required to compile with C++ */
%}

%token DIGIT

%%

line:	expr '\n' { printf("%d\n", $1); }
	;

expr:	expr '+' term { $$ = $1 + $3; }
	| term
	;

term:	term '*' factor { $$ = $1 * $3; }
	| factor
	;

factor:	'(' expr ')' { $$ = $2; }
	| DIGIT
	;

%%

int yylex(void) {
  int c;
  c = getchar();
  if (isdigit(c)) {
    yylval = c - '0';
    return DIGIT;
  }
  return c;
}

void yyerror(char *s) {
  fprintf(stderr, "%s\n", s);
}

int main() {
  yyparse();
  return 0;
}