To show the name of the data series on the chart, but only once, you can follow these steps:

1. Click on the chart to select it.
2. Click on the data series that you want to label.
3. Right-click on the data series and select "Add Data Labels".
4. Right-click on the data labels and select "Format Data Labels".
5. In the "Label Options" section, check the box next to "Series Name".
6. In the "Label Position" section, select "Outside End".
7. In the "Label Contains" section, select "Value From Cells".
8. Click on the "Select Range" button and select the cell that contains the name of the data series.
9. Click "OK" to close the "Format Data Labels" dialog box.

This will add the name of the data series to the last data point in the series. If you want to change the position of the label, you can drag it to a different location on the chart.