program goto_fool_proof_format
      goto 1000
 1001 write(*,*)'Sorry! Do not understand the answer.'
 1000 write(*,*)'Please answer yes(type in 1) or no (type in 0).'
      read(*,*)i_answer
      if ((i_answer.ne.0).and.(i_answer/=1)) goto 1001
      write(*,100)i_answer
  100 format('Great! You have typed in: ',i1,'. Now try again.')
      goto 1000
      end