#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define int ll
#define oo (int)(1e17)

int32_t main() {
    cin.sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
    freopen("out1.txt", "w", stdout);
#endif
    int n;
    cin >> n;
    int a[n + 3];
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
    }
    int ans;
    for (int i = 0; i <= 63; i++) {
        int curr = (1ll << i);
        int ch = 0;
        for (int j = 1; j <= n; j++) {
            if ((curr ^ a[j]) != (curr + a[j])) {
                ch = 1;
                break;
            }
        }
        if (ch == 0) {
            ans = curr;
            break;
        }
    }
    cout << ans;
}