program one2n
 100  write(*,*)'Please type in N:'
      read(*,*) n
      m=0
      do i=1,n
        m=m+i
      end do
      write(*,*)'The answer is:',m
      write(*,*)'Again? (1=yes,0=no)'
      read(*,*) key
      if(key==0)goto 102
      goto 100
c102  continue
 102  write(*,*)'Bye!'
      end