program one2n_again
      write(*,*)'This program will do 1+2+3...+N'
 1000 write(*,*)'What is your N?'
      read(*,*)n
      m=0
      do i=1,n
        m=m+i
      end do
      write(*,*)'The answer is',m
 1001 write(*,*)'Again?(yes:1,no:0)'
      read(*,*)k
      if(k==1)goto 1000
      if(k/=0)goto 1001
      end