#include <bits/stdc++.h>
using namespace std;
const int ms = 3e5 + 5;
const long long mod = 1e9 + 7;
int a[ms];
int cnt[ms];
long long dp[10][ms];
long long fat[ms];
long long iFat[ms];
long long fExp(long long a, long long b) {
  long long ans = 1;
  while (b) {
    if (b & 1) ans = ans * a % mod;
    a = a * a % mod;
    b >>= 1;
  }
  return ans;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n;
  int hi = 0;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    hi = max(hi, a[i]);
    cnt[a[i]]++;
  }
  fat[0] = 1;
  iFat[0] = 1;
  for (int i = 1; i <= n; i++) {
    fat[i] = fat[i - 1] * i % mod;
    iFat[i] = fExp(fat[i], mod - 2);
  }
  cnt[1] = n;
  for (int i = 2; i <= hi; i++) {
    for (int j = i + i; j <= hi; j += i) {
      cnt[i] += cnt[j];
    }
  }
  for (int k = 1; k < 10; k++) {
    for (int i = hi; i > 0; i--) {
      if (cnt[i] < k) continue;
      dp[k][i] = fat[cnt[i]] * iFat[k] % mod * iFat[cnt[i] - k] % mod;
      for (int j = i + i; j <= hi; j += i) {
        dp[k][i] = (dp[k][i] + mod - dp[k][j]) % mod;
      }
    }
    if (dp[k][1]) {
      cout << k << endl;
      return 0;
    }
  }
  cout << -1 << endl;
}
