#include <bits/stdc++.h>
#pragma warning(disable : 4996)
using namespace std;
int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int N;
  cin >> N;
  string A;
  vector<long long> num(N);
  for (int i = 0; i < N; ++i) {
    cin >> A;
    if (A.size() > 11) {
      A = A.substr(A.size() - 11, A.size());
    }
    long long a = stoll(A);
    num[i] = a;
  }
  long long c = num[0];
  for (int i = 1; i < N; ++i) {
    c = c xor num[i];
  }
  cout << c;
  return 0;
}
