%{

#include <stdio.h>
#include <ctype.h>

#define YYDEBUG 1

%}

%token NUMBER

%%

command : exp				{ printf("%d\n",$1); }
	    ;

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

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

factor	: NUMBER			{ $$ = $1; }
		| '(' exp ')'		{ $$ = $2; }

%%

main()
{
	extern int yydebug;
	yydebug = 0;
	
	return yyparse();
}

int yylex(void)
{
	int c;
	
	while((c = getchar()) == ' ');	/* 忽略空格 */
	
	if(isdigit(c)){
		ungetc(c,stdin);
		scanf("%d",&yylval);
		return(NUMBER);
	}

	if(c == '\n') return 0;	/* 停止 */
	
	return c;
}

/* 打印错误信息 */
int yyerror(char* s)
{
	fprintf(stdout, "%s\n", s);
	return 0;
}