use std::io::Read;

fn main() {
    let mut s : String = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let mut ans = -1;
    for i in s.as_str().chars() {
        if i == '0' { continue } else { ans += 1 }
    }
    println!("{}", ans - 1);
}