private int getHiFriendsNumber(String lessonString) {
int index = HI_FRIENDS_PREFIX.length();
String year = StringUtils.substring(lessonString, index, index + 1);
return Integer.parseInt(year);
}
private int getLessonNumber(String lessonString) {
int index = HI_FRIENDS_PREFIX.length() + 1 + 1 + LESSONS_PREFIX.length();
String lesson = StringUtils.substring(lessonString, index, index + 1);
return Integer.parseInt(lesson);
}