Group occurences and combine values for Line Chart

I want to create a chart that counts occurrences from two different columns which might not have the same values.

Here is a sample data:

Be aware that the unique values might not be the same in each column (in this example, "Start Week" does not have "5")

The expected result is similar to the image below.

The straight line is for "Start Week" and the squigly one is for "Finish Week".

This appears to be a simple task, but I've struggled a lot in my attempts... 😅
Thank you!