//Author: Stefan Toman

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class StefanBM {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int a[] = new int[n];
        for(int a_i=0; a_i < n; a_i++){
            a[a_i] = in.nextInt();
        }
        
        int mask = 0;
        for(int t: a) {
            mask ^= t;
        }
        System.out.println(mask);
    }
}

add bitmap solution to lonelyinteger