func detectCapitalUse(word string) bool {
	n := len(word)
	if n <= 1 {
		return true
	}
	up, lo := 0, 0
	for _, r := range word {
		if 'a' <= r && r <= 'z' {
			lo++
		} else if 'A' <= r && r <= 'Z' {
			up++
		}
	}
	return (up == 1 && 'A' <= word[0] && word[0] <= 'Z') || up == 0 || lo == 0
}