Add new KPI rows based on calculation of other 2 KPI values

Hi, I have a requirement to compute a KPI “Other COGS” based on the formula:

Other COGS = Gross Profit - Gross Margin.

This KPI calculation is to be grouped by Country, BU, Period and the new set of KPI rows would then need to be appended with existing table of rest of KPI values.

Existing table example:

| Country | BU | Period | KPI          | Value |
| A       | A  | Q1     | Revenue      | 600   |
| A       | A  | Q1     | Gross Margin | 500   |
| A       | A  | Q1     | Gross Profit | 400   |
| A       | A  | Q1     | FCF          | 100   |
| A       | A  | Q2     | Revenue      | 1600  |
| A       | A  | Q2     | Gross Margin | 1500  |
| A       | A  | Q2     | Gross Profit | 1200  |
| A       | A  | Q2     | FCF          | 1100  |
| A       | B  | Q4     | Revenue      | 2100  |
| A       | B  | Q4     | Gross Margin | 2000  |
| A       | B  | Q4     | Gross Profit | 1860  |
| A       | B  | Q4     | FCF          | 1600  |

Desired Output:

| Country | BU | Period | KPI          | Value |
| A       | A  | Q1     | Revenue      | 600   |
| A       | A  | Q1     | Gross Margin | 500   |
| A       | A  | Q1     | Gross Profit | 400   |
| A       | A  | Q1     | FCF          | 100   |
| A       | A  | Q1     | Other COGS   | -100  |
| A       | A  | Q2     | Revenue      | 1600  |
| A       | A  | Q2     | Gross Margin | 1500  |
| A       | A  | Q2     | Gross Profit | 1200  |
| A       | A  | Q2     | FCF          | 1100  |
| A       | A  | Q2     | Other COGS   | -300  |
| A       | B  | Q4     | Revenue      | 2100  |
| A       | B  | Q4     | Gross Margin | 2000  |
| A       | B  | Q4     | Gross Profit | 1860  |
| A       | B  | Q4     | FCF          | 1600  |
| A       | B  | Q4     | Other COGS   | -140  |

Please advise the best nodes to use for this case. Any help would be much appreciated as a beginner. Thanks !!