fn main() {
    let mut nm = String::new();
    std::io::stdin().read_line(&mut nm).ok();
    let nm: Vec<usize> = nm.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let mut cards: Vec<usize> = (1..=nm[0]).rev().collect();
    let mut a = String::new();
    std::io::stdin().read_line(&mut a).ok();
    a.trim().split_whitespace().map(|s| s.parse::<usize>().unwrap()).for_each(|i| {
        let v = cards.remove(nm[0] - i);
        cards.push(v);
    });

    println!("{}", cards.pop().unwrap());
}