public static int marsExploration(String s) {
        String sos = "SOS";
        int totalChangedLetters = 0;
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) != sos.charAt(i % 3)) {
                totalChangedLetters++;
            }
        }
        return totalChangedLetters;
    }