class MyLinkedList:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.head = None
        self.length = 0
        
        
    def get(self, index: int) -> int:
        """
        Get the value of the index-th node in the linked list. If the index is invalid, return -1.
        """
        if index >= self.length:
            return -1
        cur = self.head
        for i in range(index):
            cur = cur['next']
        return cur['val']
    

    def addAtHead(self, val: int) -> None:
        """
        Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list.
        """
        new_node = {}
        new_node['val'] = val
        new_node['next'] = self.head
        self.head = new_node
        self.length += 1
        

    def addAtTail(self, val: int) -> None:
        """
        Append a node of value val to the last element of the linked list.
        """
        new_node = {}
        new_node['val'] = val
        new_node['next'] = None
        curr = self.head
        for i in range(self.length-1):
            curr = curr['next']
        curr['next'] = new_node
        self.length += 1
        

    def addAtIndex(self, index: int, val: int) -> None:
        """
        Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted.
        """
        if index > self.length:
            return
        
        if index == 0:
            self.addAtHead(val)
            return
        
        new_node = {}
        new_node['val'] = val 
        prev_node = self.head
        for i in range(index-1):
            prev_node = prev_node['next']
        new_node['next'] = prev_node['next']
        prev_node['next'] = new_node
        self.length += 1
        

    def deleteAtIndex(self, index: int) -> None:
        """
        Delete the index-th node in the linked list, if the index is valid.
        """
        if index >= self.length:
            return
        
        self.length -= 1
        
        if index == 0:
            self.head = self.head['next']
            return
        
        curr = self.head
        for i in range(index):
            prev = curr
            curr = curr['next']
        prev['next'] = curr['next']


# Your MyLinkedList object will be instantiated and called as such:
# obj = MyLinkedList()
# param_1 = obj.get(index)
# obj.addAtHead(val)
# obj.addAtTail(val)
# obj.addAtIndex(index,val)
# obj.deleteAtIndex(index)