#include <bits/stdc++.h>
using namespace std;
using ull = uint64_t;

int main() {
  int n;
  cin >> n;
  ull t = (ull(1) << 63) - 1;
  for (int i = 0; i < n; i++) {
    ull a;
    cin >> a;
    t &= ~a;
  }
  for (int i = 0;; i++) {
    if (t & (ull(1) << i)) {
      cout << (ull(1) << i) << "\n";
      return 0;
    }
  }
}