#include <bits/stdc++.h>
using namespace std;
long long POW(long long A, long long N, long long MOD) {
  if (N == 0) return 1 % MOD;
  if (N == 1) return A % MOD;
  long long tmp = POW(A, N / 2, MOD) % MOD;
  if (N % 2)
    return ((tmp * tmp) % MOD * A % MOD) % MOD;
  else
    return (tmp * tmp) % MOD;
}
long long MUL(long long A, long long B, long long MOD) {
  long long r = 0;
  while (B) {
    r = (r + (A * (B % 2) % MOD)) % MOD;
    A = (A + A) % MOD;
    B /= 2;
  }
  return r;
}
long long GCD(long long A, long long B) { return B == 0 ? A : GCD(B, A % B); }
int dx[] = {0, -1, 0, 1, 0};
int dy[] = {0, 0, 1, 0, -1};
template <class X, class Y>
bool minimize(X &x, const Y &y) {
  X eps = 1e-9;
  if (x > y + eps) {
    x = y;
    return true;
  } else
    return false;
}
template <class X, class Y>
bool maximize(X &x, const Y &y) {
  X eps = 1e-9;
  if (x + eps < y) {
    x = y;
    return true;
  } else
    return false;
}
template <class T>
T Abs(const T &x) {
  return (x < 0 ? -x : x);
}
const int MAXN = 3e5 + 105;
const int MOD = 1e9 + 7;
int N;
int A[MAXN];
struct Ckn {
  static const int MAXN = 3e5 + 1000;
  long long fac[MAXN + 1000], ifac[MAXN + 1000];
  long long POW(long long A, long long N) {
    if (N == 0) return 1;
    if (N == 1) return A % MOD;
    long long tmp = POW(A, N / 2);
    if (N % 2)
      return (tmp * tmp % MOD * A) % MOD;
    else
      return (tmp * tmp) % MOD;
  }
  void PRE(int N) {
    fac[0] = 1;
    for (int i = 1; i <= N; ++i) fac[i] = (1ll * i * fac[i - 1]) % MOD;
    ifac[N - 1] = POW(fac[N - 1], MOD - 2);
    for (int i = N - 2; i >= 0; --i)
      ifac[i] = (1ll * (i + 1) * ifac[i + 1]) % MOD;
  }
  long long CALC(long long r, long long n) {
    if (n < r) return 0;
    return fac[n] * ifac[r] % MOD * ifac[n - r] % MOD;
  }
} Ckn;
int cnt[MAXN];
int dp[12][MAXN];
void Sub(int &a, const int &b) {
  a -= b;
  if (a < 0) a += MOD;
  if (a >= MOD) a -= MOD;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  cin >> N;
  for (int i = (1), _b = (N); i <= _b; ++i) {
    cin >> A[i];
    cnt[A[i]]++;
  }
  Ckn.PRE(300005);
  for (int i = (1), _b = (300000); i <= _b; ++i) {
    for (int j = 2 * i; j <= 300000; j += i) {
      cnt[i] += cnt[j];
    }
  }
  for (int i = (1), _b = (10); i <= _b; ++i) {
    for (int j = (300000), _a = (1); j >= _a; --j) {
      dp[i][j] = Ckn.CALC(i, cnt[j]);
      for (int k = 2 * j; k <= 300000; k += j) Sub(dp[i][j], dp[i][k]);
    }
    if (dp[i][1] > 0) {
      cout << i << '\n';
      exit(0);
    }
  }
  cout << -1;
  return 0;
}
