fn main() {

use std::io::{self, Write};
let mut s: Vec<u8> = Vec::new();
s.extend_from_slice(b"hello");
s.push(b',');
write!(&mut s, " world! {}", 6 * 7).unwrap();
let mut out = io::stdout().lock();
out.write_all(&s).unwrap();
writeln!(&mut out, " [{} bytes]", s.len()).unwrap();


}