use std::collections::HashSet;
use std::io::{self, BufReader, BufWriter, Read, Write};

fn main() {
    let stdin = io::stdin();
    let mut stdin = BufReader::new(stdin.lock());
    let stdout = io::stdout();
    let mut stdout = BufWriter::new(stdout.lock());

    let mut buf = String::new();
    stdin.read_to_string(&mut buf).unwrap();

    let b: HashSet<usize> = buf
        .split_whitespace()
        .take(10)
        .map(|s| s.parse::<usize>().unwrap())
        .collect();

    for i in 1..11 {
        if !b.contains(&i) {
            writeln!(&mut stdout, "{}", i).unwrap();
            break;
        }
    }
}