program newt5
c
      logical error
      integer out
      real x
      external func
      common /inout/ out
c
      out = 6
      write(out,*) ' newton-s method'
10    write(out, 103)
      read(*, 104) x
      if (x .lt. -19.0) goto 99
      call newton(x, func, error)
      if (.not. error) write(out, 102) x
      goto 10
99    stop
102   format(/' the answer is ', f12.5)
103   format(' first guess? ' )
104   format(e10.0)
      end
      subroutine func(x, fx, dfx)
c
c -- the solution for f(x) = exp(x) - 4x
c
      real x, fx, dfx, e
c
      e = exp(x)
      fx = e - 4.0 * x
      dfx = e - 4.0
      return
      end