????????
      +---------
XNTVH | QTMTUWVP
       -QRQPM
        =====
         HUJGW
        -VQWRZ
         =====
         NQMYTV
        -NXMJUW
         ======
          NWGLHP
         -NWYPLU
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard
hints: N * 2 != 0