In the GDP formula, why are Imports (I) subtracted rather than simply ignored?

GDP = total production of goods and services by Country A

C = total consumption of Country A’s produced goods and services

I = total investment in Country A’s produced goods and services

X = total exports of Country A’s produced goods and services

I = total imports of Country B’s goods and services

Thus, I should be ignored, not subtracted.

For example, suppose Country A produces 100 chairs, and also imports 30 chairs from Country B. Country A still produced 100 chairs. It didn’t produce 100 – 30 = 70 chairs.

So why is I subtracted rather than ignored?

Thank you.