fn main(){
	let mut s = String::new();
	std::io::stdin().read_line(&mut s).unwrap();
	let vec: Vec<&str> = s.trim().split(' ').collect();
	for i in 0..10 {
		if i >= 9 {
			println!("10");
			break;
		}
		let n: usize = vec[i].parse().unwrap();
		if n != i+1 {
			println!("{}", i+1);
			break;
		}
	}
}