#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>


int main(int argc, char **argv){
    int fd;
    char *file;
    file = (argc > 2) ? argv[1] : "/dev/stdin";
    fd = open(file, O_RDONLY);
    char addr[] = {0,0,0,0,0,0};
    read(fd, addr, 6);
    int i = 0;
    goto digits;
    while(i < 6){
	printf(":");
      digits:
	printf("%02x", addr[i] & 0xff);
		i++;
    }
    printf("\n");
    return 0;
}