density plot: skip first two lines

density.p

@@ -3,4 +3,4 @@ list = system(glob)
 print list
 set datafile separator ','
 unset key
-plot for [file in list] file using 2:3 w l lw 2 lc rgb "#F00000FF"
+plot for [file in list] file using 2:3 every ::2 w l lw 2 lc rgb "#F00000FF"