#include <bits/stdc++.h>
using namespace ::std;
const long double PI = acos(-1);
const long double golden = (1 + sqrt(5)) * 0.5;
int v[] = {0,   4,   22,  27,  58,  85,  94,  121, 166, 202, 265,
           274, 319, 346, 355, 378, 382, 391, 438, 454, 483, 517,
           526, 535, 562, 576, 588, 627, 634, 636, 645, 648, 654};
int main() {
  int n;
  cin >> n;
  int ans, x;
  int maximo = INT_MIN;
  for (int i = 1; i < n; i++) {
    cin >> x;
    maximo = max(maximo, x);
  }
  cin >> x;
  maximo = max(maximo, x);
  cout << (int)(x ^ maximo) << endl;
  return 0;
}
