Remove Duplicates from List

You are given a list of integers. Your task is to remove all duplicate elements from the list while preserving the order of the first occurrence of each element.

Example: For the input list [4, 5, 6, 4, 5, 6, 7], the expected output is [4, 5, 6, 7].

Note: If the list is empty, the output should be empty as well.

The solution should satisfy the following requirement in terms of time complexity:

$$ O(n) $$

inputFormat

The input is provided via stdin as a single line containing space-separated integers. If there are no integers, the input will be an empty string.

For example:

4 5 6 4 5 6 7

outputFormat

Output to stdout a single line with the list of integers (after removing duplicates) printed in the order of their first occurrence, separated by a single space. If the list is empty, output nothing.

For example:

4 5 6 7

## sample

4 5 6 4 5 6 7

4 5 6 7