#![allow(unused_variables)]
fn main() {
    use std::collections::BTreeMap;
    let mut map = BTreeMap::new();
    map.insert(3, "c");
    map.insert(2, "b");
    map.insert(1, "a");
    for (key, value) in map.iter() {
        println!("{key}: {value}");
    }
    let (first_key, first_value) = map.iter().next().unwrap();
    assert_eq!((* first_key, * first_value), (1, "a"));
}