What does this Rust snippet output?

1trait Doubler {
2    fn val(&self) -> i32;
3    fn doubled(&self) -> i32 { self.val() * 2 }
4}
5struct N(i32);
6impl Doubler for N {
7    fn val(&self) -> i32 { self.0 }
8}
9fn apply(d: &dyn Doubler) -> i32 {
10    d.doubled()
11}
12fn main() {
13    println!("{}", apply(&N(21)));
14}