#include <bits/stdc++.h>
using namespace std;
inline long long power(long long a, long long b) {
  long long x = 1;
  a = a % 1000000007ULL;
  while (b) {
    if (b & 1) x = (x * a) % 1000000007ULL;
    a = (a * a) % 1000000007ULL;
    b >>= 1;
  }
  return x;
}
inline long long inv(long long a) { return power(a, 1000000007ULL - 2); }
long long gcd(long long a, long long b) { return a ? gcd(b % a, a) : b; }
const int N = 3e5 + 5;
int n, cnt[N];
long long fac[N], invfac[N];
long long dp[9][N];
void pre() {
  fac[0] = 1;
  for (long long i = 1; i <= 300000; i++)
    fac[i] = (fac[i - 1] * i) % 1000000007ULL;
  invfac[300000] = inv(fac[300000]);
  for (long long i = 300000; i >= 1; i--)
    invfac[i - 1] = (i * invfac[i]) % 1000000007ULL;
}
long long ncr(long long n, long long r) {
  if (r < 0 || r > n) return 0;
  long long res =
      (((fac[n] * invfac[r]) % 1000000007ULL) * invfac[n - r]) % 1000000007ULL;
  return res;
}
int main() {
  ios_base::sync_with_stdio(false);
  pre();
  cin >> n;
  int x;
  for (int i = 0; i < n; i++) {
    cin >> x;
    cnt[x]++;
  }
  for (int i = 1; i <= 300000; i++)
    for (int j = 2 * i; j <= 300000; j += i) cnt[i] += cnt[j];
  for (int l = 1; l <= 8; l++) {
    for (long long i = 300000; i >= 1; i--) {
      dp[l][i] = ncr(cnt[i], l);
      for (int j = 2 * i; j <= 300000; j += i) {
        dp[l][i] = (dp[l][i] - dp[l][j] + 1000000007ULL) % 1000000007ULL;
      }
    }
    if (dp[l][1] > 0) {
      cout << l << endl;
      return 0;
    }
  }
  cout << "-1\n";
  return 0;
}
