Count the end teams

Problem

A node with no children is an end team. Print how many end teams the chart has.

Input: Line 1: the tree in level order, values separated by spaces, with null for a missing child.
Output: One integer: the number of leaves.
Constraints: 0 ≤ number of nodes ≤ 3000
-1000 ≤ each value ≤ 1000

Example 1

Input

1 2 3 4 5 null 6

Output

The leaves are 4, 5 and 6.

Example 2

Input

Output

Try the problem first. Open one hint at a time.

Hint 1

A leaf has no left and no right child.

Hint 2

Add the leaves of both sides, and count the node itself when it has no children.

Write your Python code, run it on the examples and submit it to hidden tests.