????????
      +---------
NNGMX | NYUFXHFG
       -NNGMX
        =====
         WGTJH
        -QYGRH
         =====
          ULGJF
         -RPMWR
          =====
           PGWWG
          -PNUQT
           =====
           ?????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard