graph - align data point

Hi,

I'm trying to create a graph describing the table in the attached document.

The values of "series1", "series2", "series3" describe the timings of some experiment, when different values of k are provided.

The k values are 1,51,101,...501, and are the coordinates of the x-axis.

How can I set the coordinates of x-axis to be 1,50,100,...,500 but align the data points to their real values (1,51,101,...)?