public static void countUsedHJs(Data data) throws WeFuckedUpException {
        int usedHJs = 0;
        for (Subject thisSubject : data.subjects) {
            for (Semester thisSemester : thisSubject.semesters) {
                if (thisSemester.usedState != UsedState.none) {
                    usedHJs++;
                }
            }
        }

        if (usedHJs != 35) {
            throw new WeFuckedUpException();
        }
    }