#include <bits/stdc++.h>
// #include <boost/range/irange.hpp>
// #define RANGE_1(e) (boost::irange(0,(e)))
// #define RANGE_2(s,e) (boost::irange((s),(e)))
// #define RANGE_3(s,e,step) (boost::irange((s),(e),(step)))
// #define RANGE_SELECTER(_1,_2,_3,SELECT,...) SELECT
// #define range(...) RANGE_SELECTER(__VA_ARGS__, RANGE_3, RANGE_2, RANGE_1) (__VA_ARGS__)
// #define guard(x) if(x);
#define CINS(x) for(auto&& __E__:(x))cin>>__E__;
#define ALL(x) (x).begin(),(x).end()
#define RALL(x) (x).rbegin(),(x).rend()
#define CALL(x) (x).cbegin(),(x).cend()
#define MAX(x) *max_element(ALL(x))
#define MIN(x) *min_element(ALL(x))
#define BIT(n) (1LL<<(n))

using namespace std;
using lint = long long;

template<class T>class irange{private:struct I{T x;T operator*(){return x;}bool operator!=(I&lhs){return x<lhs.x;}void operator++(){++x;}};I i,n;public:irange(T i,T n):i({i}),n({n}){}I&begin(){return i;}I&end(){return n;}};
template<class T>class srange{private:struct I{T x,s;T operator*(){return x;}bool operator!=(I&lhs){if(s<(T)0)return x>lhs.x;return x<lhs.x;}void operator++(){x=x+s;}};I i,n;public:srange(T i,T n,T s):i({i,s}),n({n,s}){}I&begin(){return i;}I&end(){return n;}};
template<class T>irange<T>range(T n){return irange(0,n);}template<class T>irange<T>range(T i,T n){return irange(i,n);}template<class T>srange<T>range(T i,T n,T s){return srange(i,n,s);}
template<class T>bool amax(T &a,const T &b){if(a<b){a=b;return 1;}return 0;}
template<class T>bool amin(T &a,const T &b){if(a>b){a=b;return 1;}return 0;}

struct initialize{initialize(){cin.tie(nullptr);ios::sync_with_stdio(false);};}__ini__;

int main(){
    /* Code Area */

    int n;
    cin >> n;
    
    vector<int> a(n);
    CINS(a);

    int maxX = 0;

    for (int i : range(n)) {
        for (int j : range(i + 1, n)) {
            amax(maxX, a[i] ^ a[j]);
        }
    }

    cout << maxX << endl;
}