Calculated field to count the number of times in approval status

Hi everyone,

I have an issue that I can't solve by myself, so maybe you can help me with your great expertise?

I need to calculate the number of times when Task was sent to Waiting for Approval status. I have a calculated field with formula IF(Status='WFA',SUM(1,Number of Times In Approval),Number of Times In Approval)

It works good, except the cases when I directly change the status from New to Awaiting for Approval. Instead of 1 it shows value 2.

Do you maybe know how I can solve it? Thank you!