use std::io::*;
use std::str::FromStr;

fn main() {
    exec(read())
}

fn exec(s: String) {
    let mut sum = s.parse::<i64>().unwrap();
    for _ in (1..99).rev() {
        if sum / 10 == 0 {
            break;
        }
        sum = calc_sum(sum.to_string());
    }
    println!("{}", sum);
}

fn calc_sum(s: String) -> i64 {
    let r = s
        .chars()
        .map(|c| c.to_digit(10).unwrap())
        .collect::<Vec<u32>>()
        .iter()
        .fold(0, |sum, a| sum + a);
    let d: i64 = From::from(r);
    d
}

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}