program test
      implicit none
c
      integer n
      real*4 result
      real*4, external :: sfak
c
      do
      write(*,*) "enter n:"
      read(*,*) n
c
      result = sfak(n)
      write(*,*) 'n=',n,' n!=',result
      enddo
c
      stop 
      end
c
c
c
      real function sfak(n)
      implicit none
      integer, intent(in) :: n
c
      integer i
c
      if(n .le. 1) then
       sfak = 1.e0
       return
      else
       sfak = 1.e0
       do i=2,n
        sfak = sfak*float(i)
       enddo
      endif
      return
      end