Gnuplot: How to plot the sum of the previous column value to the next column value till (n-1) summs (desired plot values) of my (n) column values?

Question

I have this .conv file (like a .txt file):

        0     -3.39778780952e+00     -3.64444458026e+00     -6.13098312717e+00     -3.33731379258e+00      9.6095841547