#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

FILE	*in,*out;

main(
int	argc,
char	*argv[]
)
{
extern	char	*optarg;
extern	int	optind,opterr,optopt;
	int	opcion;
	int	i,j;
	int	first,step,last;
	int	number,idx;
	char	line[1024];

	in = stdin;
	out = stdout;
	first = 1;
	step = 1;
	last = 1000000;
	number = 0;
	while ( (opcion=getopt(argc,argv,"f:l:s:n")) != EOF)
	{
		switch(opcion)
		{
			case 'f':
				first = atoi(optarg);
				break;
			case 'l':
				last = atoi(optarg);
				break;
			case 's':
				step = atoi(optarg);
				break;
			case 'n':
				number = 1;
				break;
			default:
				fprintf(stderr,
				"Uso: %s [-n][-f first][-l last][-s step]\n",
				argv[0]);
				exit(1);
		}
	}
	first = (first < 1 ? 1 : first);
	step = (step < 1 ? 1 : step);
	last = (last < first ? first : last);

	if (optind<argc)
	{
		in = fopen(argv[optind],"r");
		optind++;
	}
	if (optind<argc)
	{
		out = fopen(argv[optind],"w");
		optind++;
	}

	for (i=1; i<first && !feof(in); i++) fgets(line,1024,in);
	idx = 0;
	while(fgets(line,1024,in) != NULL)
	{
		if (number)
			fprintf(out,"%0.5d ",idx++);
		fputs(line,out);
		for (j=1; j<step && !feof(in); j++)
			fgets(line,1024,in);
	}

	fclose(in);
	fclose(out);
}