The court in Woods only mentioned the prohibition in Section 3651 to illustrate that it was not met with the problem which troubled the court in Jones v. United States, 419 F.2d 593 (8 Cir. 1969); namely, that if the sentence for armed robbery of a post office under 18 U.S.C.A. ยง 2114 were deemed mandatory, a defendant found guilty could be placed on probation or given a suspended sentence but could not be made eligible for parole prior to service of one-third of the twenty-five year sentence. 484 F.2d at 139.