Problem finding a complex formula

Hi, I'm a noob over here, I was doing a excel sheet to autocalculate the altitude of a terrain and I have the next problem:

On the Sheet I have the following data:

Some Distances Called "Progresiva en el Plano (Pg) (13:14A)

These will go on each 20 meters From Range (A15:A Infinite)

Then On top I put the data so that I will calculate the Slope (P) depending on the (Pg,X) (Cell Range C4:C9)

Then the problem arraises, and I can't find a formula for the next scenario:

the " Progresiva Absoluta (Pr)" data will sum 20 to the cell before that, up to the (Pg) value reach (Pg,X), then after that value, the (Pr) values will start at 20 again.

On Cell A:42 stops and gives + 20 m (Notice it should be + 540 m not + 20 m)

I used this formula but I'm confused of how can I applay MATCH, INDEX and VLOOKUP to this.

I Used the next formula: but I got messed up:

=IF(A16=VLOOKUP(B15,C4:C9,1,FALSE),B15+20,IF(A16>SMALL(C$4:C$9,1+COUNTIF(C$4:C$9,"<="&B15)),20,IF(A16=SMALL(C$4:C$9,2+COUNTIF(C$4:C$9,"<="&B15)),B15+20,B15+20)))

Any help regarding of a way (or a done formula that I can just drag down and keep calculating as I have more Values of (Pg,X)

find the attached file

Welcome to the forum.

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@nflsales

Maybe you can (in the future) also add the formula on the forum, so other forummembers don't have to look at the given solution.

Mr oeldere, i couldn't get you