I have a table with rows of certain email id (email ids of people subscribing to our product) and their respective start date (start date of subscribing)

The table looks some thing like this:

Let's say my 30-day cycle is from 27th May to 25th June.

Now I want to single KPI (one single number) representing count of email id in last 30 days which should be '6'.

I followed the following steps:

1. I created a calculated parameter count_email:  COUNT([Email])

2. dragged the dimension 'Startdate' to columns and changed it to day

3. dragged the count_email measure to rows and added quick table calculation of 'RUNNING TOTAL'

4. dragged the dimension 'Startdate' to filters -> selected relative filters -> to last 30 days

It shows me a line graph like this (the numbers are the actual numbers):

Although I only want one single number i.e. 3864 which is the sum of total number of subscription on 31st day.

I want to include this KPI in my dashboard.

Something like this:

And if I hover over the 31st day value i.e. 3864 and select 'keep only' it shows me a number which is the count of only 31st day and not sum till 31st day.

How can I achieve what I want?

P.S. I am not allowed to share the workbook.