program zbrac_main

      real func, x1, x2
      logical succes
      external func

      write(*,*) 'Please guess the range of root(s), x1 and x2:'
      read(*,*) x1, x2

      call zbrac (func,x1,x2,succes)

      if (succes) then
        write(*,201) x1,x2
 201    format (1x, 'There is at least one root between', f10.4,4x,'and'
     &f10.4)
      endif

      end




      function func(x)
      real func,x
      func = x**3
      end