Total sales of a chart

Problem

Each node of a chart stores the sales of one team, which may be negative after refunds. Print the total over all nodes.

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

Example 1

Input

5 3 8 1 4 7 9

Output

5 + 3 + 8 + 1 + 4 + 7 + 9 = 37.

Example 2

Input

null

Output

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

Hint 1

The sum of a missing child is 0.

Hint 2

Add the node's value to the sums of the two sides.

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