import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int i = 1;
		for ( ; i <= 9; i++) {
			int n = sc.nextInt();
			if (n == i) {
				continue;
			} else {
				System.out.println(i);
				break;
			}
		}
		if (i == 10) {
			System.out.println(10);
		}
		sc.close();
	}
}