Level by level

Problem

Print the tree one level per line. Each line holds the values of one level from left to right, separated by spaces.

Input: Line 1: the tree in level order, values separated by spaces, with null for a missing child. The tree has at least one node.
Output: One line for each level.
Constraints: 1 ≤ number of nodes ≤ 3000
-1000 ≤ each value ≤ 1000

Example 1

Input

3 9 20 null null 15 7

Output

3
9 20
15 7

Three levels.

Example 2

Input

Output

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

Hint 1

A queue holds the nodes of the current level.

Hint 2

Replace it by the children of those nodes after printing.

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