func flipLights(n int, m int) int {
	// 1. Flip all;
	// 2. Flip odd;
	// 3. Flip even;
	// 4. Flip 3k + 1.
	// So, 1 + 2 -> 3, we have 8 states at most:
	// On; 1; 2; 3; 4; 1 + 4; 2 + 4; 3 + 4.
	// When 2 < n and 3 <= m, we can have them all.
	switch {
	case m == 0:
		return 1
	case n == 1:
		return 2
	case n == 2 && m == 1:
		return 3
	case n == 2 || m == 1:
		return 4
	case m == 2:
		return 7
	}
	return 8
}