// // Created by yamunaku on 2020/02/11. // #include <bits/stdc++.h> using namespace std; #define rep(i, n) for(int i = 0; i < (n); i++) #define repl(i, l, r) for(int i = (l); i < (r); i++) #define per(i, n) for(int i = ((n)-1); i >= 0; i--) #define perl(i, l, r) for(int i = ((r)-1); i >= (l); i--) #define all(x) (x).begin(),(x).end() #define MOD9 998244353 #define MOD1 1000000007 #define IINF 1000000000 #define LINF 1000000000000000000 #define SP <<" "<< #define CYES cout<<"Yes"<<endl #define CNO cout<<"No"<<endl #define CFS cin.tie(0);ios::sync_with_stdio(false) #define CST(x) cout<<fixed<<setprecision(x) using ll = long long; using ld = long double; using vi = vector<int>; using mti = vector<vector<int>>; using vl = vector<ll>; using mtl = vector<vector<ll>>; using pi = pair<int, int>; using pl = pair<ll, ll>; template<typename T> using heap = priority_queue<T, vector<T>, function<bool(const T, const T)>>; ll gcd(__uint128_t x, __uint128_t y){ if(y == 0) return x; ll sz; while(x % y){ sz = x % y; x = y; y = sz; } return y; } int main(){ // CFS; int n; cin >> n; int lg = 0, sz = 1; while(n > sz) lg++, sz *= 2; vector<__uint128_t> a(sz, 0); ll y = 0; rep(i, n){ ll x; cin >> x; a[i] = x; if(a[i] == -1){ y |= i; a[i] = 0; } } if(y==sz-1){ cout << -1 << endl; return 0; } rep(t, lg){ rep(i, sz){ if((i & (1 << t)) == 0){ a[i] += a[i ^ (1 << t)]; } } } rep(i, sz){ a[i] = a[i] * a[i]; } rep(t, lg){ rep(i, sz){ if((i & (1 << t)) == 0){ a[i] -= a[i ^ (1 << t)]; } } } __uint128_t ans = a[0]; repl(i, 1, n){ ans = gcd(ans, a[i]); } ll ans2 = ans; if(ans2 == 0) cout << -1 << endl; else cout << ans2 << endl; return 0; }