fn getline() -> String{
        let mut __ret=String::new();
        std::io::stdin().read_line(&mut __ret).ok();
        return __ret;
}

fn main(){
        let s = getline();
        let bstr:Vec<&str>=s.trim().split(' ').collect();
        let mut bint:[usize; 9] = [0; 9];
        let mut i = 0;
        while i < 9 {
                bint[i] = bstr[i].parse().unwrap();
                i += 1;
        }
        bint.sort();
        i = 1;
        while i <= 10 {
                if i == 10 {
                        println!("{}", 10);
                        break;
                } else if bint[i-1] != i {
                        println!("{}", i);
                        break;
                }
                i += 1;
        }
}