#include <iostream>
#include <vector>

int solve (std::vector<int> a)
{
    int lonely = 0;
    for (auto i: a)
    {
        lonely ^= i;
    }
    return lonely;
}

int main() {
    std::vector<int> v;
    int n, num;
    
    std::cin >> n;
    for (int i = 0; i < n; i++)
    {
        std::cin >> num;
        v.push_back(num);
    }
    
    std::cout << solve (v) << std::endl;
    
    return 0;
}