#include <bits/stdc++.h>
using namespace std;
const long long N = 300050;
long long n, cnt[N];
long long dp[20][N];
long long mod = 1000000007;
long long fact[N];
long long inv[N];
long long combination(long long a, long long b) {
  if (a < b) return 0;
  return ((1ll * fact[a] * inv[b]) % mod * inv[a - b]) % mod;
}
void sub(long long &a, long long b) {
  a -= b;
  if (a < 0) a += mod;
}
long long bin_pow(long long a, long long b) {
  long long ret = 1;
  while (b) {
    if (b & 1) ret *= a;
    a *= a;
    ret %= mod;
    a %= mod;
    b >>= 1;
  }
  return ret;
}
signed main() {
  ios::sync_with_stdio(0);
  fact[0] = 1;
  for (long long i = 1; i < N; i++) {
    fact[i] = (fact[i - 1] * i) % mod;
  }
  inv[N - 1] = bin_pow(fact[N - 1], mod - 2);
  for (long long i = N - 1; i >= 1; i--) {
    inv[i - 1] = (inv[i] * i * 1ll) % mod;
  }
  cin >> n;
  for (long long i = 0; i < n; i++) {
    long long a;
    cin >> a;
    cnt[a]++;
  }
  for (long long i = 1; i < N; i++) {
    for (long long j = 2 * i; j < N; j += i) cnt[i] += cnt[j];
  }
  for (long long i = 1; i < 8; i++) {
    for (long long j = N - 1; j >= 1; j--) {
      dp[i][j] = combination(cnt[j], i);
      for (long long k = 2 * j; k < N; k += j) sub(dp[i][j], dp[i][k]);
    }
    if (dp[i][1] > 0) return cout << i << '\n', 0;
  }
  cout << -1;
  return 0;
}
