use std::cmp::*;
use std::collections::*;
use std::io::*;
use std::str::FromStr;
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")
}
fn main(){
    let mut n:i64 = read();
    let mut tmp:i64 = 0;
    while n / 10 > 0 {
        let mut k = n;
        while(k > 0){
            tmp += k % 10;
            k /= 10;
        }
        n = tmp;
        tmp = 0;
    }
    println!("{}",n);
}