fn main() {
    //標準入力処理は https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 より引用
    let s = {
        let mut s = String::new();
        std::io::stdin().read_line(&mut s).unwrap();
        s.trim_right().to_owned()
    };
    let mut v = 0;
    for i in 0..s.len() {
        let n: u32 = s.chars().nth(i).unwrap() as u32;
        v += n - 48;
    }
    println!("{}", v);
}