int start = 0;
boolean startMarked = false;
char[] chars = input.toCharArray();
List<String> strings = new ArrayList<>();
for (int i = 0 ; i < input.length() ; ++i) {
    boolean number = Character.isDigit(chars[i]);
    if (!startMarked && number) {
        startMarked = true;
        start = i;
    } else if (!number && startMarked) {
        strings.add(input.substring(start, i));
        startMarked = false;
    }
}
Character[] resultChars = strings.stream().map(str -> (char)Integer.parseInt(str)).collect(Collectors.toList()).toArray(new Character[]{});
char[] resultArray = new char[resultChars.length];
for (int i = 0 ; i < resultChars.length ; ++i) {
    resultArray[i] = resultChars[i];
}
return new String(resultArray);