fn main() {
    let v: Vec<char> = input_line::<String>()[0].chars().collect();
    let mut ans = 0;
    for ch in &v[1..] {
        if *ch != '0' {
            ans += 1;
        }
    }
    print!("{}", ans);
}

fn input_line<T: std::str::FromStr>() -> Vec<T> {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}