A few formulas will fix the data for you. Columns A and B contain your original data. Columns C thru F have formulas in these cells, copied down as far as needed:
D2: (not formulas, just values 1, 2, 3, etc.)
Just plot columns E and F in your chart.
If you have the new Dynamic Arrays, it's even easier. Columns A and B have the original data. These formulas are only entered into the indicated cells, and they fill values down automagically: