import java.util.Scanner;

class no481{
	public static void main(String[] args) {
		Scanner stdIn=new Scanner(System.in);
		int b[]=new int[9],i;
		for(i=0;i<9;i++) b[i]=stdIn.nextInt();
		for(i=0;;i++) if(b[i]!=i+1) break;
		System.out.print(i+1);
	}
}