#include<bits/stdc++.h>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
#define rep(i,n) for(int i=0; i<(n); i++)

int N;
int A[2000];

int main() {
  cin>>N; rep(i,N) cin>>A[i];
  int ans=0; rep(i,N) rep(j,i) ans=max(ans,A[i]^A[j]);
  cout<<ans<<endl;
  return 0;
}