#include <bits/stdc++.h>
using namespace std;
 
#define rep(i,j,n) for(int i=j;i<n;++i)
#define all(i) i.begin(),i.end()
#define rall(i) i.rbegin(), i.rend()
#define INF 1e9
#define LINF 1e18
// const int mod = 998244353;
const int mod = 1000000007;
 
using i64 = long long;
using pi = pair<int, int>;
 
template <class T> using vt = vector<T>;
template <class T> using vvt = vector<vector<T>>;
 
i64 gcd(i64 n, i64 m) {return (m == 0? n : gcd(m, n % m));}
i64 lcm(i64 n, i64 m) {return (n / gcd(n, m) * m);}
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n;
  cin >> n;
  vt<i64> a(n);
  rep(i, 0, n) cin >> a[i];

  i64 x = 1;
  rep(i, 0, 62) {
    bool ok = true;
    rep(j, 0, n) {
      if((x + a[j]) != (x ^ a[j])) ok = false;
    }
    if(ok) return cout << x << endl, 0;
    x *= 2;
  }
}