Adding a variable range to a formula, depending on values

I've cracked my head thinking, searching, trying and failing.

Attached you will find an example of the file.

In the INPUT, I paste a set of data. The first CALC set I use to swap columns Distance and Height.
In the FIXED section, there are a number of fixed values every 10 meters.

The final CALC section is used to calculate the nearest values below and above the fixed value for each KP, along with its height. The problem is that when pasting other INPUT data, there could be more or less points for each KP. In this example, I have 5 points at KP0 and 4 points at KP10. But the next INPUT could very well contain 10 KP0 and 6 KP10 values and so on...

My question is: is there a way to automatically determine the range of the values at KP0, KP10, ... so I don't have to manually select it every time I copy data in this sheet? If so, how do I set up the formula to calculate the nearest distances with this range?

Please keep in mind that the KP limit could reach around 3000.


Very much obliged.

Thanks

I swap them to determine the height for the corresponding value for Distance A at the far right with VLOOKUP.

The fixed distances for the different KP's are given. The purpose of the excel sheet is to calculate the height at this given KP, but unfortunately the INPUT data rarely has this exact value. So I want to calculate the interpolated height out of the two nearest values for each KP.

A million times thanks! Just what I needed!