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

int solve() {
    int N; cin >> N;
    if (N == 1) return 0;
    vector<int> a(N);
    for(int i = 0; i < N; i++) cin >> a[i];
    int res = 0;
    for (int i = 0; i < 31; i++) {
        int bit = 1 << i;
        int val = bit & a[0];
        for (int j = 1; j < N; i++) {
            if (val != (bit & a[i])) {
                res += bit;
                break;
            }
        }
    }
    return res;
}
int main() {
    cout << solve() << endl;
}