import java.util.*;

class Main {
	static Scanner sc = new Scanner(System.in);
	public static void main(String[] args) {
		
		for (int i=1; i<=10; i++) {
			if (sc.nextInt() != i) {
				System.out.println(i);
				return;
			}
			if (i == 10) System.out.println(10);
		}
		
	}
}