The Handshake Party

Party tradition: every guest shakes hands with every other guest exactly once. How many handshakes? 🤝

You get the number of guests. Print the total handshakes. Simulate with two loops — then see if you can spot the formula hiding in your answer.

Example:

Input: guests = 4 Output: 6

The pairs are (1,2), (1,3), (1,4), (2,3), (2,4), (3,4) — 6 handshakes total.