Death Circle

Forty men found themselves in a desperate situation, and all but two of them decided that they should kill themselves.  Unable to dissuade the group, the two men who refused to give up pretended to go along with the group's plan.  They even suggested a way in which death can take place in an orderly manner.  

Here is their idea: all forty men should sit in a circle, and, starting with someone who wanted to go first, every third person in the circle would follow; the counting would go around till the last man, who should commit suicide.  The two men thought that if they placed themselves at certain points in the circle, all others in the group would have died before them.  For their scheme to work, where in the circle should they sit?    >>>