use std::fs::File;
use std::io::Read;
// use std::cmp;

fn digitsum(mut a: i32) -> i32 {
    let mut b = 0;
    loop{
        b += a % 10;
        a /= 10;
        if a == 0{
            break;
        }
    }
    return b;
}

fn main() {
    let inputstatus = 10;
    let mut buf = String::new();

    let filename = "inputrust.txt";

    if inputstatus == 0 {
        let mut f = File::open(filename).expect("file not found");
        f.read_to_string(&mut buf)
            .expect("something went wrong reading the file");
    } else {
        std::io::stdin().read_to_string(&mut buf).unwrap();
    }

    let mut iter = buf.split_whitespace();

    let mut n: i32 = iter.next().unwrap().parse().unwrap();
    for _ in 0..10 {
        n = digitsum(n);
    }
    println!("{}", n);

}