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

using ll = long long;
using ull = unsigned long long;
using db = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pdd = pair<db, db>;
using tiii = tuple<int, int, int>;
using str = string;

#define vt vector
#define pb push_back
#define eb emplace_back
#define ins insert
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define sz(x) (int)x.size()

#define mp make_pair
#define mt make_tuple
#define fi first
#define se second

constexpr int INFi = 2e9;

vt<ll> bits[64];

int dfs(ll cur, int depth, ll start, ll finish, unordered_set<ll> &used) {
    used.ins(cur);
    int ans = INFi;
    for (int j = 0; j < 64; j++) {
        if ((cur >> j) & 1) {
            for (ll &g : bits[j]) {
                if (!used.count(g)) {
                    if (g == finish && cur != start) {
                        return depth + 1;
                    } else {
                        ans = min(dfs(g, depth + 1, start, finish, used), ans);
                    }
                }
            }
        }
    }
    return ans;
}

void solve() {
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) {
        ll a;
        cin >> a;
        for (int j = 0; j < 64; j++) {
            if ((a >> j) & 1) {
                bits[j].pb(a);
            }
        }
    }
    int answ = INFi;
    for (int i = 0; i < 64; i++) {
        if (sz(bits[i]) >= 3) {
            cout << "3\n";
            return;
        } else if (sz(bits[i]) == 2) {
            unordered_set<ll> used;
            answ = min(answ, dfs(bits[i][0], 1, bits[i][0], bits[i][1], used));
        }
    }
    cout << (answ == INFi ? -1 : answ) << '\n';
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    // freopen("input.txt", "r", stdin);
    // freopen("output.txt", "w", stdout);
    int tests = 1;
    // cin >> tests;
    while (tests--) {
        solve();
    }
    return 0;
}