Help with pivot chart

[Ronyn]

Hello,

please look at the attached table. It is very simple table with 3 columns. The real one has thousands of rows and I would like to make the chart using the pivot table and chart if possible without modify the table.
The first column is the date and each row is the related month. The second column is the company name and the third column is the turnover of the company for the related month.
I would like to create a chart in wich on x-axis there are the months and the company name, on y-axis the values their turnover. Imagine now that the real table has hundreds of different companies.
The idea is to use a chart with lines. One line will be the total turnover of all the companies, the second line will be a group of companies (eg. A+B in this case, but they can be more together) , the third line will be only one company (eg. in this case C).

How to do it without modifying the data in the excel table?