Order pizza for your SF meetup! aka my first Rust program

soma_pizza.rs

use std::io;

fn main() {
    println!("How many RSVPS do you have for your Meetup?");

    let mut input = String::new();
    io::stdin().read_line(&mut input)
        .expect("Failed to read input.");
    let trimmed = input.trim();

    let rsvps = trimmed.parse::<u32>().expect("Must input an integer.");
    let num_pies = calc_num_pies(rsvps);

    println!("Order {} x-large pies from SOMA Pizza!", num_pies);
}

// Formula graciously provided by Rob Durst
fn calc_num_pies(rsvps: u32) -> u32 {
    let x_large_factor = 0.8;
    let num_attendees = (rsvps as f32) * 0.33;
    let num_slices = num_attendees * 2.0;
    let num_pies = ((num_slices / 8.0) * x_large_factor).round() as u32;
    if num_pies < 1 {
        return 1;
    };
    return num_pies;
}