#include <iostream>
#include <algorithm>
#include <iterator>
#include <vector>

using namespace std;

int main() {
    int n;
    cin>>n;
    vector <int> v(n);
    copy_n (istream_iterator <int> (cin), n, v.begin());
    cout<<*find_if (v.begin(), v.end(), [v](int &el){
        return count (v.begin(), v.end(), el) == 1;
     });
    return 0;
}