For any $N$, let $f(N)$ be the last twelve hexadecimal digits before the trailing zeroes in $N!$.

For example, the hexadecimal representation of $20!$ is 21C3677C82B40000,
so $f(20)$ is the digit sequence 21C3677C82B4.

Find $f(20!)$. Give your answer as twelve hexadecimal digits, using uppercase for the digits A to F.