#include<cstdio>
#include<iostream>
#include<cstring>
using namespace std ;

#define maxn 100001

int n ;

int v[maxn] ;

int sumaxor ;

void afisare_sol()
{

}

int main()
{

    freopen("joc3.in", "r", stdin);
    freopen("joc3.out", "w", stdout);

    scanf("%d", &n);

    bool ok = false ;

    for(int i = 1; i <= n; ++i )
    {
        scanf("%d", &v[i]);

        if( v[i] > 0 && i < n )
            ok = true ;
    }

    if( ok == false )
    {
        printf("-1\n");
        return 0 ;
    }

    for(int i = 1; i <= n; i += 2 )
        sumaxor ^= v[i] ;

    if( sumaxor == 0 )
        printf("-1\n");
    else
        afisare_sol() ;

    return 0 ;

}