use proconio::input;

fn main() {
    input!{
        s: String,
    };

    let mut count = 0;
    if &s[0..1] == "1" {count += 1}
    if &s[1..2] == "1" {count += 1}
    if &s[2..3] == "1" {count += 1}
    println!("{}", count);
}
