#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int n;
  cin >> n;
  vector<ll> a(n);
  rep(i, n) cin >> a[i];
  ll ans = 0;
  rep(_, 62) {
    ll ans = 1LL << _;
    bool ok = true;
    rep(i, n) {
      if ((a[i] ^ ans) != a[i] + ans) ok = false;
    }
    if (ok) {
      cout << ans << endl;
      return 0;
    }
  }
  return 0;
}