#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++){
        mapa.insert(pair<long long,long long>(i+1,0));
    }

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

        scanf("%llu",&aux);

        mapa.find(aux)->second++;
    }

    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;
}