import java.util.*;
class Test24{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int[] num = new int[9];
		
		for(int i=0; i<num.length; i++){
			num[i]= sc.nextInt();
		}
		
		for(int j=1; j<=9; j++){
			if(num[j-1] != j){
				System.out.println(j);
				break;
			}else{
				System.out.println("10");
				break;
			}
		}
	}
}