#include <iostream>
#include <cstdio>
#include <map>
using namespace std;
map<int, int> NUM;
int main(){
int n;
while(1){
NUM.clear();
scanf("%d", &n);
if(n == 0)
break;
int num;
for(int i = 0; i < n; i++){
scanf("%d", &num);
NUM[num] += 1;
}
map<int, int>::iterator it;
it = NUM.begin();
for(; it != NUM.end(); it++){
int k = it->second;
if(k % 2){
cout << it->first << endl;
break;
}
}
}
return 0;
}