#include <iostream>
#include <string>
#include <cmath>
#include <algorithm>
#include <iomanip>
#include<cstdio>
#include<algorithm>
using namespace std;
int main()
{
	int n,a,ans,i;
	cin >> n >> ans;
	for(i = 2;i <= n;i++)
	{
		cin >> a;
		ans ^= a;
	}
	cout << ans;
	return 0;
}