What are the exact odds of getting a royal flush with spades?

Had a question on a math test which was about the odds of getting a full house. I figured (52/52 * 3/51 * 2/50 * 48/49 * 3/48), which is 1 in 6941.666… Obviously not right.

I did (52/52 * 3/51 * 2/50 * 49/49 * 3/48), 1 in 6800, and that’s what I put.

But doesn’t my 4th card have to be 48/49, since it can be ANY card, except the one remaining in the deck with the value of the first 3 cards, which would give me four of a kind?