use std::io::{self, BufRead};

const N: [&str; 9] = ["1", "2", "3", "4", "5", "6", "7", "8", "9"];

fn get_lines() -> Vec<String> {
    let stdin = io::stdin();
    let lines: Vec<String> = stdin.lock().lines().map(|l| l.unwrap()).collect();
    return lines;
}

fn main(){
    let s = &get_lines()[0];
    for (i, s) in s.split(' ').enumerate() {
        if s != N[i] {
            println!("{}", N[i]);
            return;
        }
    }
    println!("10");
}