fn main() {
    let arr = [1, 2, 5];
    let slice = &arr;
    for i in slice {
        println!("w {}", i);
    }
    for j in arr {
        println!("ww {}", j);
    }
    let first = slice.get(0).unwrap();
    let last = if slice.get(3).is_some() {
        slice.get(3).unwrap()
    } else {
        &-1
    };

    println!("f {} l {}", first, last);
}