Combined COUNTIF for several columns

Simplified task: We have table with values like this

I need a formula for cell D1 to count rows that have in column A value "one" and column B is not empty.

For example:

• in first row A1==one but B1 is empty; (that doesn`t count)


• in second row A2==one and B2 is not empty; (that counts 1)


• ...


• in 4th row A4 is not equal to value "one" (that doesn`t count)

I know about formulas like COUNTIF and COUNTIFS but I can`t figure out how to use them with combined condition.

Thanks in advance.