fn main() {
    let mut aa = String::new();
    std::io::Read::read_to_string(&mut std::io::stdin(), &mut aa).ok();
    let aa: Vec<u64> = aa.split_whitespace().skip(1).flat_map(str::parse).collect();

    let n = aa.len() as u64;
    let mut seq = 0;

    for &a in aa.iter().rev() {
        if a == n - seq {
            seq += 1;
        }
    }

    println!("{}", n - seq);
}