A conversation between User and Assistant. The user asks a question, and the Assistant solves it. The assistant first thinks about the reasoning process in the mind and then provides the user with the answer.
User: Find the common rule that maps an input grid to an output grid, given the examples below.

Example 1:
Input:  5 5 6 5 8 7 3 1 0 0 0 0 0 0 0 6 8 4 1 5 4
Output: 6 5 8 7 3 1 0 0 0 0 0 0 0 6 8 4 1 5 4 5 5

Example 2:
Input:  1 8 7 9 8 9 1 4 3 9 1 5 7 5 0 0 7 3 6 5 6
Output: 7 9 8 9 1 4 3 9 1 5 7 5 0 0 7 3 6 5 6 1 8

Example 3:
Input:  8 8 8 6 5 9 4 8 3 0 0 0 0 0 0 0 0 0 0 7 9
Output: 8 6 5 9 4 8 3 0 0 0 0 0 0 0 0 0 0 7 9 8 8

Below is a test input grid. Predict the corresponding output grid by applying the rule you found.
Input:
0 0 0 0 2 4 4 6 0 0 0 0 0 0 0 0 0 0 0 0 0
Show your work in <think> </think> tags, and return the answer in <answer> </answer> tags with space between each number. For example <answer> 1 3 5 7 </answer>.
Assistant: Let me solve this step by step.
<think>
user