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