#include <iostream>
#include <sstream>
#include <cerrno>

using namespace std;

void count_down(int n);
int  get_starting_val_from_args(int argc, char *argv[]);
void usage_abort(string progname, int err);

int main(int argc, char *argv[])
{
	int n = get_starting_val_from_args(argc, argv);

	count_down(n);

	return 0;
}

int  get_starting_val_from_args(int argc, char *argv[])
{
	istringstream ss;
	int           n;

	if (argc != 2)
		usage_abort(argv[0], EINVAL);
	ss.clear();
	ss.str(argv[1]);
	if ((ss >> n) == NULL) {
		cerr << "Argument must be an integer" << endl;
		usage_abort(argv[0], EINVAL);
	}
	return n;
}

void usage_abort(string progname, int err)
{
	cerr << "Usage:  "
	     << progname << " n" << endl;
	exit(err);
}

void count_down(int n)
{
        if (n == 0)
                cout << "Blastoff!" << endl;
        else {
                cout << n << endl;
                count_down(n - 1);
        }
}