Get the total sum of IGST values in a set of Invoices

I need to fetch the count of occurrence of the word ‘IGST’ in a set of invoices. If the count is greater than 1, then i need to get the sum of the IGST values and i need to return the final IGST value. Is there any way to resolve this requirement?

How you are extracting IGST values from set of invoices. It can help to investigate to get the solution.
If you already extraction in excel at a particular column the it can be possible.

provide the sample workflow file and output to better understand

I’m trying getting IGST by applying RegEx in Matches activity using the expression (?<=IGST).*
But the problem is that it isn’t getting IGST accurately.
Is there any solutions other than RegEx for this?
I need to sum up multiple IGST values and write the net value to an excel sheet