Grouping multiple columns as single series for pivot table

Hi all,
Hoping you can help me out. I need to merge multiple columns into a single series for use in a pivot table and chart.
See below:

Data source (table):
Example.png

Pivot table and chart:
Example 2.png

As you can see, each patient (defined as a unique row in data source) will have multiple Dates of Service (DOS) over the course of their treatment. I need to be able to tally how many patients appeared at each date of service. In this case, the patient must be counted as a unique count for each DOS. For example, patient John Smith needs to be counted twice - once in the DOS 4/23 count, and again in the DOS 7/22 count.

What is the most efficient way to do this? Is it even possible ?

Thank you in advance and happy to clarify further if my explanation was not clear.