import java.util.Scanner;

public class Answer {
	public static void main(String str[]) {
        Scanner sc = new Scanner(System.in);

        for(int i=1; i<=9; i++) {
        	if(i != Integer.valueOf(sc.next())) {
        		System.out.println(i);
        		return;
        	}
        }
        System.out.println(10);
	}
}