use std::collections::HashMap;
use std::time::{SystemTime, Duration};

fn main() {
    let mut sessions: HashMap<&str, SystemTime> = HashMap::new();
    sessions.insert("session1", SystemTime::now());
    sessions.insert("session2", SystemTime::now() - Duration::from_secs(3600));
    sessions.insert("session3", SystemTime::now() - Duration::from_secs(7200));

    // Retain only sessions that are less than an hour old
    let one_hour = Duration::from_secs(3600);
    sessions.retain(|_id, &mut timestamp| {
        timestamp.elapsed().unwrap_or_default() < one_hour
    });

    println!("{:?}", sessions); // Output: Only sessions less than an hour old
}