WYGH
      +---------
GYQPU | HRNFMWFF
       -GYQPU
        =====
        YWYPWW
       -WPTHJR
        ======
         NXUJHF
        -NYGGNU
         ======
          UXTLLF
         -UMWUNX
          ======
           YYMXY

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: medium