#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
using f64 = double;
using f80 = long double;
using pii = pair<int, int>;
using pll = pair<i64, i64>;
using ptx = pair<f64, f64>;
const int N = 3e5 + 5, LG = 20;
int f[N], conv[N], tmp[N];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
  int n;
  cin >> n;
  for (int t, i = 1; i <= n; ++i) {
    cin >> t;
    f[t] = conv[t] = 1;
    if (t == 1) {
      cout << "1\n";
      return 0;
    }
  }
  for (int tid = 2; tid <= 7; ++tid) {
    i64 drop, st, dr;
    for (int i = N - 1; i >= 1; --i) {
      drop = st = dr = 0;
      for (int j = i; j < N; j += i) {
        drop += tmp[j];
        st += conv[j];
        dr += f[j];
      }
      tmp[i] = st * dr - drop;
    }
    if (tmp[1]) {
      cout << tid << endl;
      return 0;
    }
    for (int i = 0; i < N; ++i) {
      conv[i] = int(tmp[i] > 0);
      tmp[i] = 0;
    }
  }
  cout << "-1\n";
  return 0;
}
