program main
  implicit none
  integer*8::N,upper,i,j
  integer*8,allocatable::furui(:)
  read *,N
  do
     if(MOD(N,2).eq.1) exit
     N = N/2
  end do
  upper = INT(SQRT(DBLE(N)+1))
  allocate(furui(3:upper))

  furui = 0
  do i=3,upper,2
     if(furui(i).ne.0) cycle
     if(MOD(N,i).eq.0) then
        print '(i0)',i
        return
     end if
     do j=i+i,upper,i
        furui(j) = 1
     end do
  end do
end program main