import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		
		int frnd = 0;
		
		for(int i=0; i<N; i++) {
			int nfrnd = sc.nextInt();
			frnd ^= nfrnd;
		}
		System.out.println(frnd);
		sc.close();

	}

}