Padding for Same Convolution

Problem Statement

Determine the padding $P$ required to keep the output size equal to the input size (assuming stride S=1).

Background

To maintain spatial dimensions ($O = I$) with stride 1, we solve:

$I = I - F + 2P + 1$

This gives us: $P = \frac{F - 1}{2}$

This is called "same" padding because the output has the same spatial dimensions as the input.

Your Task

Write a function calculate_same_padding(filter_size) returning the integer padding amount. Assume the filter size is always odd.

Output Format

Return an integer representing the padding needed for "same" convolution.