text: #include <vector>
  #include <set>
  #include <iostream>
  #include <limits>
  
  using namespace std;
  
  
  int findLonelyInt(const vector<int> &A)
  {
      set<int> s;
     
      int v = 0; 
      for (vector<int>::const_iterator it = A.begin(); it != A.end(); ++it) {
          v = *it;
          if (s.count(v) == 0) {
              s.insert(v);
          } else {
              s.erase(v);
          }
      }
  
      if (s.size() != 1) {
          cout << "ERR: Size == " << s.size() << endl;
      }
  
      return *s.begin();
  }
  
  int main(void)
  {
      int N = 1;
      cin >> N;
  
      if (((N % 2) != 1)  || (N >= 100)) {
          cerr << "Bad input specification, N must be odd and < 100." << endl;
          return -1;
      }
  
      cin.ignore(numeric_limits<streamsize>::max(), '\n');
      vector<int> A;
      int tmp = 0;
      for (int i = 0; i < N; ++i) {
          cin >> tmp;
          A.push_back(tmp);
      }
      int li = findLonelyInt(A);
      cout << li << endl;
  
      return 0;
  }
  