fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: Vec<char> = n.trim().chars().collect();

    if n.len() >= 2 && n[0] == '1' && n[1..].iter().all(|&c| c == '3') {
        println!("{}", n.len() - 1);
    } else {
        println!("-1");
    }
}