#include<iostream>

#include<stdio.h>

using namespace std;

int main()

{

    int len;

    while(cin>>len)

    {

        int ans;

        len--;

        cin>>ans;

        while(len--)

        {

            int a;

            cin>>a;

        ans=ans^a;

        }

        cout<<ans<<endl;

    }

    system("pause");

    return 0;

}