#include <bits/stdc++.h>
using namespace std;
const int N = 3 * 1000 * 100 + 10, mod = 1LL * 1000 * 1000 * 1000 + 7;
int n, fact[N], inv[N], dp[N][15], cnt[N];
long long Pow(long long a, long long b) {
  return b ? (b & 1 ? a : 1) % mod * Pow(a * a % mod, b >> 1) % mod : 1;
}
int C(int r, int n) {
  if (r > n) return 0;
  return 1LL * fact[n] * inv[r] % mod * inv[n - r] % mod;
}
int main() {
  cin >> n;
  fact[0] = 1;
  for (int i = 1; i < N; i++) fact[i] = 1LL * fact[i - 1] * i % mod;
  inv[N - 1] = Pow(fact[N - 1], mod - 2);
  for (int i = N - 2; i >= 0; i--) inv[i] = 1LL * inv[i + 1] * (i + 1) % mod;
  for (int i = 0, a; i < n; i++) {
    cin >> a;
    for (int j = 1; j * j <= a; j++)
      if (a % j == 0) {
        cnt[j]++;
        if (a / j != j) cnt[a / j]++;
      }
  }
  for (int j = 1; j <= 10; j++) {
    for (int i = N - 1; i >= 1; i--) {
      dp[i][j] = C(j, cnt[i]);
      for (int k = 2 * i; k < N; k += i)
        dp[i][j] = ((dp[i][j] - dp[k][j]) % mod + mod) % mod;
    }
    if (dp[1][j]) return cout << j << '\n', 0;
  }
  cout << "-1\n";
  return 0;
}
