fn main() {
    let mut n = read::<i64>();
    for _ in 0..100 {
        let ns = format!("{}", n);
        n = ns
            .chars()
            .map(|x| x.to_digit(10).unwrap() as i64)
            .sum::<i64>();
    }
    println!("{}", n);
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}