#include <bits/stdc++.h>

using namespace std;

/*map<long long,long long>mapa;

int main()
{
  long long i,n,aux;

  scanf("%llu",&n);

  while(n!=0){

    mapa.clear();

    for(i=0;i<n;i++){

        scanf("%llu",&aux);

        mapa.insert(pair<long long,long long>(aux,0));
        mapa.find(aux)->second++;
    }

    /*for (map<long long,long long>::iterator it=mapa.begin(); it!=mapa.end(); ++it)
     {

            cout<<"chave = "<<it->first<<" "<<" valor = "<<it->second<<"\n";

     }*/

    /*long long resp = 0;

     for (map<long long,long long>::iterator it=mapa.begin(); it!=mapa.end(); ++it)
     {
         if(it->second % 2 != 0){
            resp = it->first;
         }
     }

    printf("%llu\n",resp);

    scanf("%llu",&n);
  }
  return 0;
}*/

#define max 100000

long long B[max];

int main()
{
    long long ones,twos,x,i,n;

    scanf("%llu",&n);

    while(n!=0){

        ones = twos = 0;

        memset(B,0,n*sizeof(long long));

        for(i=0;i<n;i++){
            scanf("%llu",&B[i]);
        }

       for(i=0;i<n;i++){
            x =  B[i];
            ones ^= x;
        }

        printf("%llu\n", ones );

        scanf("%llu",&n);
    }

    return 0;

}