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

	enum {
		S0, S1, S2, S3, S4
	} state;

	state = S0;

	for (p = s; *p != '\0'; p++) {
		switch (state) {
		case S0: /* start */
			switch ((unsigned char) *p) {
			case 'M': state = S1; break;
			default:  return -1; /* leaf */
			}
			break;

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

		case S2: /* e.g. "Mr" */
			switch ((unsigned char) *p) {
			case 's': state = S3; break;
			case '.': state = S4; break;
			default:  return -1; /* leaf */
			}
			break;

		case S3: /* e.g. "Mrs" */
			switch ((unsigned char) *p) {
			case '.': state = S4; break;
			default:  return -1; /* leaf */
			}
			break;

		case S4: /* e.g. "Mr." */
			return -1; /* leaf */

		default:
			; /* unreached */
		}
	}

	/* end states */
	switch (state) {
	case S4: return 0x1; /* "M(r|rs)\." */
	default: return -1; /* unexpected EOT */
	}
}