#include<bits/stdc++.h>

using namespace std;

#define ll long long
#define all(a) a.begin(),a.end()
#define endl '\n'

int main()
{
    ios::sync_with_stdio(0); cin.tie(0);
   ll n;cin>>n;
   ll ans=1;
   ll x;
   cin>>x;
   ans=x;
   for(ll i=1;i<n;i++)
   {
    cin>>x;
    ans^=x;
   }
   cout<<ans<<endl;
}