import java.util.*;

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