use std::io;
use std::io::prelude::*;

fn main() {
    let mut s: String = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let stdout = io::stdout();
    let mut stdout = io::BufWriter::new(stdout.lock());

    let n: u32 = s.trim()
        .chars()
        .map(|c| c.to_digit(10)
        .unwrap())
        .sum();
    writeln!(stdout, "{}", n).unwrap_or(());
}