program rtsafe_main
      real rtsafe, x1, x2, xacc
      external rtsafe, funcd

      write (*,*) 'Please type in interval x1 and x2 :'
      read (*,*) x1, x2
      write(*,*) 'Please typle in theaccuracy for root finding :'
      read (*,*) xacc
      
      write(*,*) 'The root is ', rtsafe(funcd,x1,x2,xacc)
      write(*,*) 'within the accuracy of +/-  ', xacc

      end


c     subroutine funcd(x,f,df)
c     real x, f, df
c     f = x**3
c     df = 3*(x**2)
c     end


      subroutine funcd(x,f,df)
      real x, f, df
      f = x**2 - 1.0
      df = 2*x
      end


c     subroutine funcd(x,f,df)
c     real x, f, df
c     f = 7*sin(x) + x
c     df = 7*cos(x) + 1
c     end