memory008

#include <fstream>
#define ULL unsigned long long int
using namespace std;
ifstream f("memory008.in");
ofstream g("memory008.out");
ULL x,nr;

int main()
{
    int n;
    f>>n;
    for(int i=0;i<n;++i)
        f>>x,nr^=x;
    g<<nr;
    return 0;
}