public static int countAlreadyUsed(Data myData){
        int usedHjs = 0;
        for(int subjectNo=0; subjectNo<12; subjectNo++){
            for(int hj=0; hj<4; hj++){
                if (myData.subjects[subjectNo].semesters[hj].usedState != Semester.UsedState.none){
                    usedHjs++;
                }
            }
        }
        return usedHjs;
    }