#include<bits/stdc++.h>
using namespace std;
int a[10001];
int main(){
	//freopen("","r",stdin);
	//freopen("","w",stdout);
	int n,x,sum;
	cin>>n; 
	cin>>a[1];
	sum=a[1];
	for(int i=2;i<=n;i++){
		cin>>a[i];
		sum^=a[i];
	}
	cout<<sum<<endl;
	return 0;
}