First, there are 26 distinct alphabets and 10 distinct digit numbers.
Then, the first digit of ID has 26 possibilities.
For the rest of 2 digits, the total cases are 10*10 = 100 possibilities.
However, there are 10 cases are repeated when two digits are the same. so you have to subtract it by 10
So answer will be 26 * (100-10) = 23400
