import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        for(int i=1; i<=9; i++){
            int tmp = sc.nextInt();
            if(tmp!=i){
                System.out.println(i);
                System.exit(0);
            }
        }
        System.out.println(10);
    }
}