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:  2 1 9 2 4 8 2 3 0 0 0 0 0 0 0 0 0 4 3 3
Output: 4 8 2 3 0 0 0 0 0 0 0 0 0 4 3 3 2 1 9 2

Example 2:
Input:  6 8 5 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 8
Output: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 8 6 8 5 1

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

Below is a test input grid. Predict the corresponding output grid by applying the rule you found.
Input:
2 7 3 9 8 3 2 0 0 4 5 7 4 7 8 3 6 9 9 4
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