????????
      +---------
4DBD0 | 45912C99
       -4DBD0
        =====
         C550C
        -4DBD0
         =====
         649D99
        -668BAA
         ======
          D37DD9
         -D311B4
          ======
          ??????

base: 14
letters: 0123456789ABCD
difficulty: hard