#include <bits/stdc++.h>
using namespace std;
int sdf[30] = {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};
long long int a[71720], b, c, d, n, m, i, j, k, sum, sumend;
bool cmp(int a, int b) { return a > b; }
int gcd(int a, int b) {
  if (!b) return a;
  return gcd(b, a % b);
}
int gqt(int n) {
  if (!n || n) return 0;
  if (n == 2) return 1;
  for (int i = 3; i <= sqrt(n); i++)
    if (n % i == 0) return 0;
  return 1;
}
int main() {
  cin >> n;
  for (i = 1; i <= n; i++) cin >> a[i];
  sum = a[n];
  sort(a + 1, a + n + 1);
  sumend = a[n];
  cout << (sumend ^ sum) << endl;
  return 0;
}
