function LinkedList() { 
  var length = 0; 
  var head = null; 

  var Node = function(element){ // {1} 
    this.element = element; 
    this.next = null; 
  }; 

  this.size = function(){
    return length;
  };

  this.head = function(){
    return head;
  };

  this.add = function(element){
    var node = new Node(element);
    if(head === null){
        head = node;
    } else {
        currentNode = head;

        while(currentNode.next){
            currentNode  = currentNode.next;
        }

        currentNode.next = node;
    }

    length++;
  }; 

  this.remove = function(element){
    var currentNode = head;
    var previousNode;
    if(currentNode.element === element){
        head = currentNode.next;
    } else {
        while(currentNode.element !== element) {
            previousNode = currentNode;
            currentNode = currentNode.next;
        }

        previousNode.next = currentNode.next;
    }

    length--;
  };

  // Only change code below this line
  this.removeAt = function(index){
      var currentNode = head;
      var previousNode;
      if(index < 0 || index >= this.size()){
          return null;
      }
      
      var i = 0;
      if(index == 0){
          head = currentNode.next;
      }else{
          
          while(i < index){
              previousNode = currentNode;
              currentNode = currentNode.next;
              i++;
          }
          
          previousNode.next = currentNode.next;
          
      }
      
      length--;
      return currentNode.element;
  }
  // Only change code above this line
}