def add_word(w, node=root):
    
    car = w[0]
    global num_nodi
    num_nodi = num_nodi +1
    
    if node.next.has_key(car):
        n = node.next[car]
        if len(w) == 1:
            if not n.isterminal: n.isterminal = True 
            return 

        add_word(w[1:], n)

    else:
        if len(w) == 1:
            node.next[car] = Node(car,1)
            return 
            
        else:
            node.next[car] = Node(car)
            add_word(w[1:], node.next[car])
    
    return