????????
      +---------
7A627 | C7C7DDD2
       -7A627
        =====
        31DDBD
       -338564
        ======
         9619DD
        -9074A7
         ======
          236DB2
         -3C8377
          ======
          ??????

base: 14
letters: 0123456789ABCD
difficulty: hard