import java.util.NoSuchElementException;
import java.util.Scanner;

public class No481 {

    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        for (int i = 1; i <= 10; i++) {
            try {
                int num = s.nextInt();
                if (i != num) {
                    System.out.println(i);
                    return;
                }
            } catch (NoSuchElementException ex) {
                System.out.println(i);
            }
        }
    }
}