/* Given a string, return a new string where "not " has been added to the front. 
However, if the string already begins with "not", return the string unchanged. 
Note: use .equals() to compare 2 strings. */
 
public String notString(String str) {
    if((str.length() >= 3) && (str.substring(0,3).equals("not"))){
        return str;
    } else {
        return "not " + str;
    }
}