????????
      ----------
PUUMP ) NPGGNFQY
       -UJPPX
        =====
        PPNNHF
       -PJUREF
        ======
         PJFXJQ
        -PJUREF
         ======
           NQJYY
          -NUNFU
           =====
           ?????

base: 13
symbols: EFGHJMNPQRUXY
difficulty: medium