use std::io::Read;

fn main() {
    let mut buf = String::new();
    std::io::stdin().read_to_string(&mut buf).unwrap();
    
    let mut iter = buf.split_whitespace();
    
    let mut n: usize = iter.next().unwrap().parse().unwrap();
    let lengths = iter.rev()
        .map(|l| l.parse::<usize>().unwrap());
    
    for length in lengths {
        if length == n {
            n -= 1;
        }
    }
    
    println!("{}", n);
}