Insert total at variable intervals

Hi all

Been trying to solve this problem by using a formula to automate the insertion of totals in Sheet1 (column F) of the attached workbook.

The attached workbook shows the required results using individual SUM formulas. The S*** numbers in column G have to be entered manually and the number of rows between each S*** number will vary.

The SUM total starts from either the 1st row of the sheet or the row below the previous S*** number.

I have not been able to come up with anything that works.

TIA ...spellbound