import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

    	Scanner sc = new Scanner(System.in);

    	int num = 0;

    	for(int i=1;i<=9;i++){
    		int el = sc.nextInt();
    		num = el;
    		if(el!=i){
    			break;
    		}
    	}
    	System.out.println(num);
    }

}