????????
      +---------
XXCWP | FCUJFUPF
       -XXCWP
        =====
        YQHHQU
       -YGWUQC
        ======
         CXFPPP
        -CCUYJW
         ======
          CGFWJF
         -CWJWEJ
          ======
          ??????

base: 12
letters: CEFGHJPQUWXY
difficulty: medium