class Node:
    def __init__(self, left=None, right=None):
        self.left = left
        self.right = right

    def count(self):
        # count this node
        total = 1

        # if left child exists, get its count
        if self.left is not None:
            total += self.left.count()

        # if right child exists, add its count
            total += self.right.count()

        return total

    # Hack to let us put nodes in a set
    __hash__ = object.__hash__

# Empty node
n = Node()
assert n.count() == 1

# Two children
a = Node()
b = Node()
root = Node(a, b)
assert root.count() == 3

# root.right.right is root
root = Node()   #    root
a = Node()      #  /      \
b = Node()      # a        b
c = Node()      #        /   \
                #       c   root
root.left = a
root.right = b
b.left = c
b.right = root

# Max recursion depth
root.count()