#include <bits/stdc++.h>
using namespace std;
void canhazfast() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
}
template <typename T>
T gcd(T a, T b) {
  return b ? gcd(b, a % b) : a;
}
template <typename T>
T extgcd(T a, T b, T &x, T &y) {
  T x0 = 1, y0 = 0, x1 = 0, y1 = 1;
  while (b) {
    T q = a / b;
    a %= b;
    swap(a, b);
    x0 -= q * x1;
    swap(x0, x1);
    y0 -= q * y1;
    swap(y0, y1);
  }
  x = x0;
  y = y0;
  return a;
}
int ctz(unsigned x) { return __builtin_ctz(x); }
int ctzll(unsigned long long x) { return __builtin_ctzll(x); }
int clz(unsigned x) { return __builtin_clz(x); }
int clzll(unsigned long long x) { return __builtin_clzll(x); }
int popcnt(unsigned x) { return __builtin_popcount(x); }
int popcntll(unsigned long long x) { return __builtin_popcountll(x); }
int bsr(unsigned x) { return 31 ^ clz(x); }
int bsrll(unsigned long long x) { return 63 ^ clzll(x); }
vector<int> vset;
vector<int> x[64];
bool vis[100016];
int p[100016];
int d[100016];
int q[100016];
vector<int> adj[100016];
long long a[100016];
int bfs(int s) {
  int k = 0;
  int res = 12345;
  for (int i : vset) {
    d[i] = 0;
    p[i] = 0;
    vis[i] = false;
  }
  vis[s] = true;
  q[k++] = s;
  for (int i = 0; i < k; ++i) {
    int u = q[i];
    int dv = d[u] + 1;
    for (int v : adj[u]) {
      if (v == p[u]) continue;
      if (vis[v]) {
        res = min(res, d[u] + d[v] + 1);
      } else {
        p[v] = u;
        d[v] = dv;
        vis[v] = true;
        q[k++] = v;
      }
    }
  }
  return res;
}
int main() {
  canhazfast();
  int n, ans = 12345;
  cin >> n;
  for (int i = 1; i <= n; ++i) {
    cin >> a[i];
    for (int j = 0; j < 60; ++j) {
      if ((a[i] >> j) & 1) x[j].push_back(i);
    }
  }
  for (int i = 0; i < 60; ++i) {
    if (x[i].size() >= 3) return cout << "3\n", 0;
    if (x[i].size() == 2) {
      int u = x[i][0], v = x[i][1];
      adj[u].push_back(v);
      adj[v].push_back(u);
    }
  }
  for (int i = 1; i <= n; ++i) {
    sort((adj[i]).begin(), (adj[i]).end());
    adj[i].erase(unique((adj[i]).begin(), (adj[i]).end()), adj[i].end());
  }
  for (int i = 1; i <= n; ++i) {
    if (adj[i].size()) vset.push_back(i);
  }
  for (int i : vset) ans = min(ans, bfs(i));
  if (ans >= 12345) ans = -1;
  cout << ans << '\n';
  return 0;
}
