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program main
  implicit none
  interface 
     function fib(n)
       integer, intent(in) :: n 
       integer :: fib
     end function fib
  end interface

  print *, fib(10)
end program main

recursive function fib (n)  result (fnum) 
  integer, intent(in)  :: n
  integer :: fnum
  if (n<2) then 
     fnum = n
  else
     fnum = fib(n-1) + fib(n-2)
  endif
end function fib