????????
      +---------
FQWPM | JEMUWQUF
       -FQWPM
        =====
         PUMYQ
        -FQWPM
         =====
         HHUJJU
        -WGQHJE
         ======
          YHYNJF
         -HGWPNR
          ======
          ??????

base: 13
letters: EFGHJMNPQRUWY
difficulty: hard