fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let mut a: usize = s
        .trim()
        .chars()
        .map(|c| c.to_digit(10).unwrap() as usize)
        .sum();

    for _ in 1..99 {
        a = a / 10 + a % 10;
    }
    println!("{}", a);
}