#include<iostream>
using namespace std;
int main(){
    freopen("xor_equ.in","r",stdin);
    freopen("xor_equ.out","w",stdout);
    int n;
    cin>>n;
     int max=0;
     string a;
     string c;
     for(int i=0;i<n;i++) {
         cin>>a[i];
     }
     for(int i=1;i<n;i++){
         for(int j=2;j<n;j++){
             for(int l=j-1;l>=0;l--){
                 c[1]=a[l];
                c[i]=a[i-l-1]^c[i];
                  
         }
         if(c[i]>max){
             max=c[i];
         }
             }
         }
     cout<<max; 
    return 0;
}