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class CircularDoubleLinkedList{

    public CircularDoubleLinkedList prev, next;
    public int value;
    
    
    public CircularDoubleLinkedList(int value){
        this.value = value;
        this.prev = this;
        this.next = this;
        //assert(this.checkStructure());
    }
    
    private CircularDoubleLinkedList(int value, CircularDoubleLinkedList prev, CircularDoubleLinkedList next){
        this.value = value;
        this.prev = prev;
        this.next = next;
        //assert(this.checkStructure());
    }
    
    
    public CircularDoubleLinkedList insert(int value){
        CircularDoubleLinkedList res = new CircularDoubleLinkedList(value);
        res.prev = this.prev;
        res.next = this;
        this.prev.next = res;
        this.prev = res;
        
        return res;
    }
    
    
    public int size(){
        int res = 1;
        CircularDoubleLinkedList tmp = this.next;
        while(!(tmp == this)){
            res++;
            tmp = tmp.next;
        }
        
        return res;
    }
    
    public boolean checkStructure(){
        
        CircularDoubleLinkedList tmpThisNext = this;  //Laufvariable für die Vorgänger der Elemente
        CircularDoubleLinkedList tmpThis = this;    // für die Abbruchbedingung
       
        if(tmpThis.next == null || tmpThis.prev == null){
            return false;
        }
        
        CircularDoubleLinkedList tmpPrev = this.prev; // für die letzte Überprüfung
        CircularDoubleLinkedList tmpNext = this.next;  // Laufvariable für die Elemente
        
        while(!(tmpNext == tmpThis)){
            if(tmpNext.prev != tmpThisNext) return false;
            if(tmpNext.next == null) return false;
            if(tmpNext.next == this && tmpPrev != tmpNext) return false;
            
            tmpThisNext = tmpThisNext.next;
            tmpNext = tmpNext.next;
        }
        
        return true;
    }
            
    
    
    
    public static void main(String[] args){
        CircularDoubleLinkedList c1 = new CircularDoubleLinkedList(1);
        
        System.out.println(c1.size());
        System.out.println(c1.checkStructure());
        
        c1 = c1.insert(2);
        
        System.out.println(c1.size());
        System.out.println(c1.checkStructure());
        
        c1 = c1.insert(3);
        System.out.println(c1.size());
        System.out.println(c1.checkStructure());
        
    }
    
}