The Missing Party Guest

Guests 1 through n RSVP'd; the sign-in sheet is shuffled and one guest never showed. 🎈

You get n and the shuffled sign-ins. Print the missing guest number. Elegant route: what SHOULD all the numbers add up to?

Example:

Input: n = 5, nums = [2, 5, 1, 4] Output: 3

Guests 1 through 5 should sum to 15, but the sign-in sheet only sums to 12 — the missing guest is 15 - 12 = 3.