#include <bits/stdc++.h>
using namespace std;
const int maxn = 3e5 + 5;
const int MOD = 1e9 + 7;
long long fac[maxn], inv[maxn];
long long qpow(long long a, long long b, long long mod = MOD) {
  long long res = 1;
  while (b) {
    if (b & 1) res = res * a % mod;
    a = a * a % mod;
    b >>= 1;
  }
  return res;
}
long long C(int n, int m) {
  if (n < m) return 0;
  return fac[n] * inv[m] % MOD * inv[n - m] % MOD;
}
void init() {
  fac[0] = 1;
  for (int i = 1; i <= maxn - 5; i++) fac[i] = fac[i - 1] * i % MOD;
  inv[maxn - 5] = qpow(fac[maxn - 5], MOD - 2);
  for (int i = maxn - 6; i >= 0; i--) inv[i] = inv[i + 1] * (i + 1) % MOD;
}
int n, cnt[maxn], dp[10][maxn];
int main() {
  init();
  scanf("%d", &n);
  for (int i = 1, x; i <= n; i++) {
    scanf("%d", &x);
    cnt[x]++;
    if (x == 1) return puts("1"), 0;
  }
  for (int i = 1; i <= maxn - 5; i++) {
    for (int j = i + i; j <= maxn - 5; j += i) {
      cnt[i] += cnt[j];
    }
  }
  for (int i = 2; i < 10; i++) {
    for (int j = maxn - 5; j; j--) {
      dp[i][j] = C(cnt[j], i);
      for (int k = j + j; k <= maxn - 5; k += j) {
        dp[i][j] = (dp[i][j] - dp[i][k] + MOD) % MOD;
      }
    }
    if (dp[i][1] > 0) return printf("%d\n", i), 0;
  }
  puts("-1");
  return 0;
}
