#include <bits/stdc++.h>
using namespace std;
#define REP(i, n) for(int(i)=0;(i)<(n);++(i))
int main(){
    int N; cin >> N;
    int a = -1, maxv = 0;
    REP(i,N){
        int M; cin >> M; a &= M;
        maxv = max(maxv, M);
    }
    cout << (maxv^a) << endl;
}