fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

fn main() {
  let nm:Vec<usize> = read_vec();
  let ops:Vec<usize> = read_vec();

  let mut sort = vec![None; nm[0]];
  for i in 0..nm[0] {
    sort[i] = Some(nm[0] - i);
  }

  for i in 0..ops.len() {
    let mut idx = 0;
    let mut count = 0;
    for j in 0..sort.len() {
      if sort[sort.len()-j-1].is_some() {
        count += 1;
        if count == ops[i] {
          idx = sort.len()-j-1;
          break;
        }
      }
    }
    let temp = sort[idx];
    sort[idx] = None;
    sort.push(temp);
  }

  println!("{}", sort[sort.len()-1].unwrap());
}