fn main() {
    let c = {
        let mut buf = String::new();
        std::io::stdin().read_line(&mut buf).unwrap();
        buf.trim_end().to_owned()
    };

    let mut ans = 0;
    for x in c.chars() {
        if x == '0' { continue; }
        ans += 1;
    }
    
    println!("{}", ans - 1);
}