First Pair with Target Sum

Given a list of integers and a target sum \(s\), find the first pair of integers (in order of appearance) that add up to \(s\). If no such pair exists, output None.

The pair is determined by scanning the list from left to right. For each number, if there exists a previously seen number that, together with the current number, sums to \(s\), then that pair is the answer. For example, if the list is [1, 4, 8, 7, 3, 15] and \(s = 8\), the answer is 1 7.

inputFormat

The input consists of two lines:

• The first line contains space-separated integers representing the list. (This line may be empty, in which case the list is considered empty.)
• The second line contains a single integer \(s\), the target sum.

outputFormat

Output the first pair of integers that sum up to \(s\), separated by a space. If no such pair exists, print None.

1 4 8 7 3 15
8

1 7