#include <iostream>
using namespace std;
int main() {
    int n;
    int a[2000];
    int b[2000];
    int i;
    cin >> n;
    for (i=0; i<n; i++) cin >> a[i];
    for (i=0; i<n-1; i++) b[i] = a[i]^a[i+1];
    for (i=1; i<n-1; i++) b[0] ^= b[i];
    cout << b[0];
    return 0;
}