In the statement, "any symbol" means NOT any valid ASCII char, but any byte, including those with codes 128..255. Common methods to read text in Rust, including stdin().read_line, expect valid UTF-8 and therefore crash on test 2 where bytes 128..255 are present. I got AC with this:

let mut reader = BufReader::new(stdin());
let mut s = Vec::new();
reader.read_until(10, &mut s).unwrap();