Difficulty: Medium

Long ago, the king of Puzzleonia lost the combination to the safe where the secret pretzel recipe is held. He sent for Al Krakit, the most prolific safecracker in the prison system, and offered him a royal pardon if he succeeded in opening the safe.

After several attempts at bypassing the combination, Al Krakit has realized that the only way to open the safe safely is to try every possible combination by hand. The special lock has a four-character code. Two of the characters must be letters, and the lock is case sensitive (with AB not the same as ab). The other two must be digits, anything from 0 to 9.

What is the maximum number of combinations that Al Krakit would have to try before finding the correct code?