????????
      +---------
WYZYR | JQQGGZQX
       -ZXNXZ
        =====
        PJQLUZ
       -PZHPNZ
        ======
          HXUNQ
         -RMZZW
          =====
          YVTZTX
         -YJJPGZ
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard