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public static long countVietnameseLetters(String input) {
        List<String> telexTexts =List.of("aw", "aa", "dd", "ee", "oo", "ow", "w");
        long count = 0;
        for (int i = 0; i < input.length(); i++) {
            if (i + 1 <= input.length() && telexTexts.contains(input.substring(i, i + 1))) {
                count++;
            } else if (i + 2 <= input.length() && telexTexts.contains(input.substring(i, i + 2))) {
                count++;
                i++;
            }
        }
        return count;
    }