#! /bin/sed -f

        /^[^ \t]/b process

:append
        H
        $ {
                s/.*/\n/
                b process
        }
        d

:process
        x
        /^$/ b end
        s/^\n//
        ${
          x
          /^\n$/{
            x
            p
            b empty
          }
          x
        }

:empty
        s/.*//

:end
        x
        /^\n$/d
        b append