int
fsm_main(const char *s)
{
	const char *p;

	enum {
		S0, S1, S2
	} state;

	state = S0;

	for (p = s; *p != '\0'; p++) {
		switch (state) {
		case S0: /* start */
			switch ((unsigned char) *p) {
			case '2':
			case '3':
			case '4':
			case '5':
			case '6':
			case '7':
			case '8':
			case '9': state = S1; break;
			case '1': state = S2; break;
			default:  return -1; /* leaf */
			}
			break;

		case S1: /* e.g. "2" */
			return -1; /* leaf */

		case S2: /* e.g. "1" */
			switch ((unsigned char) *p) {
			case '0':
			case '1':
			case '2': state = S1; break;
			default:  return -1; /* leaf */
			}
			break;

		default:
			; /* unreached */
		}
	}

	/* end states */
	switch (state) {
	case S1: return 0x1; /* "(1|2|3|4|5|6|7|8|9|10|11|12)" */
	case S2: return 0x1; /* "(1|2|3|4|5|6|7|8|9|10|11|12)" */
	default: return -1; /* unexpected EOT */
	}
}