// Problem#: 1200
// Submission#: 1222027
// The source code is licensed under Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License
// URI: http://creativecommons.org/licenses/by-nc-sa/3.0/
// All Copyright reserved by Informatic Lab of Sun Yat-sen University
#include<iostream>
using namespace std;
int main()
{
int n,temp,res;
while(cin >> n && n != 0)
{
res = 0;
while( n-- )
{
cin >> temp;
res ^= temp;
}
cout << res << endl;
}
return 0;
}