Simple recursive fibonacci function in Fortran

program fib
  implicit none
  integer :: i
  i = fibonacci(40)
contains
  recursive function fibonacci(n) result(fib)
    integer :: n
    integer :: fib

    if (n < 2) then
      fib = 1
    else
      fib = fibonacci(n-2) + fibonacci(n-1)
    endif
  end function fibonacci
end program fib