#include <stdio.h>
#include <string.h>
#include <pwd.h>
#include <grp.h>

int main (int argc, char *argv[])
{
	int ret = -1;
	if (argc != 2){
		fprintf (stderr,"user2group user\n");
	}else{
		const char *user = argv[1];
		struct passwd *p = getpwnam (user);
		if (p == NULL){
			fprintf (stderr,"user %s does not exist\n",user);
		}else{
			struct group *g;
			bool once = false;
			while ((g=getgrent())!=NULL){
				for (int i=0; g->gr_mem[i] != NULL; i++){
					if (strcmp(user,g->gr_mem[i])==0){
						if (once){
							printf (" ");
						}
						once = true;
						printf ("%s",g->gr_name);
						break;
					}
				}
			}
			printf ("\n");
			ret = 0;
		}
	}
	return ret;
}