c     file name : ex0202.f
      program nibunho
      parameter( imax = 20, epsilon = 1d-3 )
      f(x) = x**3 - 1.0
      write(*,*) 'Enter two values of nibunho'
      read(*,*) a, b
      do i=1, imax
        c   = 
        yac = f(a) * f(c)
        if( yac .lt. 0.0 ) then
          
        else
          
        endif
        ans   = ( a + b )/2.0
        ratio = abs( ( b - a) / ans )
        write(*,*) i, yac, a, b, ans, ratio
        if(             ) stop
      enddo
      end