package Course_Codes;

import java.util.Scanner;

//输入n和n-1个整数，输出只出现1次的个数
public class LQ_008 {

	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		int n,ans=0;//读入几个数
		
		while(sc.hasNext()) {
			 n=sc.nextInt();
			ans=0;
			for(int i=0;i<n;i++) {
				ans=ans^sc.nextInt();
			}
			System.out.print(ans);
		}
	}

}