#include <bits/stdc++.h>
using namespace std;

int a[10000010],n,i,j;
int main(){
	cin>>n;
	for(i = 0;i < n;i++){
		cin>>a[i];
	}
	
	sort(a,a+n);
	int c = 0;
	for(i = 0;i < n;i++){
		c++;
		if(i == n - 1 || a[i] != a[i + 1]){
			if(c % 2 == 1){
				cout<<a[i]<<endl;
				break;
			}
			
			c = 0;
		}
	}
}
/**************************************************************
	Problem: 1472
	User: admin
	Language: C++
	Result: Accepted
	Time:27 ms
	Memory:41140 kb
****************************************************************/