public static String shrink(String input) {
        if (input == null || input.length() == 0) return "";
        StringBuilder sb = new StringBuilder();
        char[] chars = input.toCharArray();

        sb.append(chars[0]);
        int counter = 1;
        for (int i = 1; i < chars.length; i++) {
            if (chars[i] == chars[i-1]) {
                counter++;
            } else {
                if (counter > 1) sb.append(counter);
                sb.append(chars[i]);
                counter = 1;
            }
        }
        if (counter > 1) sb.append(counter);

        return sb.toString();
    }