ring">fn main() {
</span><span class="boring">use std::thread;
</span><span class="boring">use std::time::Duration;
</span><span class="boring">
</span><span class="boring">fn simulated_expensive_calculation(num: u32) -&gt; u32 {
</span><span class="boring">    println!(&quot;calculating slowly...&quot;);
</span><span class="boring">    thread::sleep(Duration::from_secs(2));
</span><span class="boring">    num
</span><span class="boring">}
</span><span class="boring">
</span>fn generate_workout(intensity: u