#include<bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef pair<int,int> P;

#define p_ary(ary,a,b) do { cout << "["; for (int count = (a);count < (b);++count) cout << ary[count] << ((b)-1 == count ? "" : ", "); cout << "]\n"; } while(0)
#define p_map(map,it) do {cout << "{";for (auto (it) = map.begin();;++(it)) {if ((it) == map.end()) {cout << "}\n";break;}else cout << "" << (it)->first << "=>" << (it)->second << ", ";}}while(0)

ll gcd(ll a,ll b) {
    while (b) {
        a %= b;
        swap(a,b);
    }
    return a;
}

int main() {
    int n;cin >> n;
    vector<ll> a(1000000),c;
    for (int i = 0;i < n;++i) cin >> a[i];
    c = a;
    // for (int i = 0;i < 20;++i) if ((n>>i)&1) b = i;
    for (int i = 0;i < 19;++i) for (int j = 0;j < n;++j) if (!(j&(1<<i)) && c[j] > -1) {
        if (c[i|(1<<i)] > -1) c[j] += c[i|(1<<i)];
        else c[j] = -1;
    }
    ll ans = 0;
    for (int i = 0;i < n;++i) if (c[i] > -1) ans = gcd(ans,gcd(ans,a[i])*gcd(ans,c[i]));
    if (ans == 0) cout << -1 << endl;
    else cout << ans << endl;
}