Get distinct count of timeseries

Hi everyone

I am working with my prometheus datasource.
I want to count the number of times a specific alert got fired in the given time range.
So I have my annotations to place the timemarks.
And now I have this panel.
You can clearly see that there were two alerts that started in the given timerange because there are two separate time series with as value the start timestamp of the alert.
But how can i transform this to a counter that has as label the “label” that I created and has as value the count (here 2).

I would be so grateful if anyone has an idea of how to help me.
Thanks anyway!