#include <bits/stdc++.h>
using namespace std;
const long long N = 3e5 + 5, inf = 1e18, mod = 1e9 + 7;
long long n, a[N], t[N], dp[N][10], fact[N], inv[N], ted[N];
long long spow(long long a, long long b) {
  if (b == 0) return 1;
  long long c = spow(a, b / 2);
  c = c * c;
  c %= mod;
  if (b & 1) c *= a;
  return (c % mod);
}
long long C(long long x, long long y) {
  if (x > y) return 0;
  long long res = ((fact[y] * inv[x]) % mod) * inv[y - x];
  return (res % mod);
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  fact[0] = 1;
  for (long long i = 1; i < N; i++) fact[i] = (fact[i - 1] * i) % mod;
  inv[N - 1] = spow(fact[N - 1], mod - 2);
  for (long long i = N - 2; i >= 0; i--) inv[i] = (inv[i + 1] * (i + 1)) % mod;
  cin >> n;
  for (long long i = 1; i <= n; i++) {
    cin >> a[i];
    t[a[i]]++;
  }
  for (long long i = 1; i < N; i++)
    for (long long j = 1; i * j < N; j++) ted[i] += t[i * j];
  for (long long i = N - 1; i >= 1; i--) {
    for (long long j = 1; j <= 7; j++) {
      dp[i][j] = C(j, ted[i]);
      for (long long k = 2; k * i < N; k++) dp[i][j] -= dp[i * k][j];
      while (dp[i][j] < 0) dp[i][j] += mod;
    }
  }
  for (long long i = 1; i <= 7; i++)
    if (dp[1][i]) return cout << i, 0;
  cout << -1;
  return 0;
}
